List.RemoveAll() efficiency / compiler optimisation





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22















Regarding efficiency, does anyone know if the compiler is clever enough to not create the array containing 1, 3, 5 for each iteration of the loop in the following code?



var foo = new List<int> { 1, 2, 3, 4, 5 };

foo.RemoveAll(i => new { 1, 3, 5 }.Contains(i));


I prefer it for readability, but not at the sake of performance.






c# arrays list linq compiler-optimization







share|improve this question




















  • 25





    try for your self sharplab.io

    – Michael Randall
    2 days ago






  • 1





    @MichaelRandall Great site. You should write an answer for this with an short example. This is interesseting for everybody, i think.

    – kara
    2 days ago






  • 1





    I'm really surprised but it looks like it does actually create a new instance of the 3 item array for each iteration inside the method internal bool <M>b__0_0(int i).

    – maxp
    2 days ago




















22















Regarding efficiency, does anyone know if the compiler is clever enough to not create the array containing 1, 3, 5 for each iteration of the loop in the following code?



var foo = new List<int> { 1, 2, 3, 4, 5 };

foo.RemoveAll(i => new { 1, 3, 5 }.Contains(i));


I prefer it for readability, but not at the sake of performance.






c# arrays list linq compiler-optimization







share|improve this question




















  • 25





    try for your self sharplab.io

    – Michael Randall
    2 days ago






  • 1





    @MichaelRandall Great site. You should write an answer for this with an short example. This is interesseting for everybody, i think.

    – kara
    2 days ago






  • 1





    I'm really surprised but it looks like it does actually create a new instance of the 3 item array for each iteration inside the method internal bool <M>b__0_0(int i).

    – maxp
    2 days ago
















22












22








22


6






Regarding efficiency, does anyone know if the compiler is clever enough to not create the array containing 1, 3, 5 for each iteration of the loop in the following code?



var foo = new List<int> { 1, 2, 3, 4, 5 };

foo.RemoveAll(i => new { 1, 3, 5 }.Contains(i));


I prefer it for readability, but not at the sake of performance.






c# arrays list linq compiler-optimization







share|improve this question
















Regarding efficiency, does anyone know if the compiler is clever enough to not create the array containing 1, 3, 5 for each iteration of the loop in the following code?



var foo = new List<int> { 1, 2, 3, 4, 5 };

foo.RemoveAll(i => new { 1, 3, 5 }.Contains(i));


I prefer it for readability, but not at the sake of performance.






c# arrays list linq compiler-optimization




c# arrays list linq compiler-optimization






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 2 days ago









Michael Randall

37.2k84171




37.2k84171










asked 2 days ago









maxpmaxp

9,92735105175




9,92735105175








  • 25





    try for your self sharplab.io

    – Michael Randall
    2 days ago






  • 1





    @MichaelRandall Great site. You should write an answer for this with an short example. This is interesseting for everybody, i think.

    – kara
    2 days ago






  • 1





    I'm really surprised but it looks like it does actually create a new instance of the 3 item array for each iteration inside the method internal bool <M>b__0_0(int i).

    – maxp
    2 days ago
















  • 25





    try for your self sharplab.io

    – Michael Randall
    2 days ago






  • 1





    @MichaelRandall Great site. You should write an answer for this with an short example. This is interesseting for everybody, i think.

    – kara
    2 days ago






  • 1





    I'm really surprised but it looks like it does actually create a new instance of the 3 item array for each iteration inside the method internal bool <M>b__0_0(int i).

    – maxp
    2 days ago










25




25





try for your self sharplab.io

– Michael Randall
2 days ago





try for your self sharplab.io

– Michael Randall
2 days ago




1




1





@MichaelRandall Great site. You should write an answer for this with an short example. This is interesseting for everybody, i think.

– kara
2 days ago





@MichaelRandall Great site. You should write an answer for this with an short example. This is interesseting for everybody, i think.

– kara
2 days ago




1




1





I'm really surprised but it looks like it does actually create a new instance of the 3 item array for each iteration inside the method internal bool <M>b__0_0(int i).

– maxp
2 days ago







I'm really surprised but it looks like it does actually create a new instance of the 3 item array for each iteration inside the method internal bool <M>b__0_0(int i).

– maxp
2 days ago














3 Answers
3






active

oldest

votes


















13














The answer is no it doesn't optimize out the allocation of the array



Basically, every time the predicate is called, it checks against the compiler generated class and initializes a new array to call the Contains (as you can see here)



private sealed class <>c

{

    public static readonly <>c <>9 = new <>c();



    public static Predicate<int> <>9__0_0;



    internal bool <M>b__0_0(int i)

    {

        // bam!

        int obj = new int[3];

        RuntimeHelpers.InitializeArray(obj, (RuntimeFieldHandle)/*OpCode not supported: LdMemberToken*/);

        return Enumerable.Contains(obj, i);

    }

}





share|improve this answer

































    4














    As @Michael Randall already wrote, it looks like it is not possible.



    I agree, that your questioned code is nicely readable, having the list in the RemoveAll method. But to have the instance only once, I have three ideas of doing it:



    int a = null;
    
foo.RemoveAll(i => (a ?? (a = new { 1, 3, 5 })).Contains(i));


    This is actually yours, with little un-beatuness of needing an external variable.



     foo = foo.Except(new { 1, 3, 5 }).ToList();


    That's actually pretty nice solution using Linq.



     new List<int>{1, 3, 5}.ForEach(x => foo.Remove(x));
    

    

    
 new {1, 3, 5}.Iterate(x => foo.Remove(x));


    This is something I'd do. In neary all of my code I have my Extension method "Iterate" to avoid the need of foreach. And also, i dont want to "toList" everything all the time to make a .ForEach(..)



    static class Extensions
    
{
    
    public static void Iterate<TSource>(this IEnumerable<TSource> source, Action<TSource> action)
    
    {
    
        foreach (var item in source)
    
        {
    
            action.Invoke(item);
    
        }
    
    }
    
}





    share|improve this answer



















    • 5





      Beware, RemoveAll performs vastly better that multiple calls to Remove.

      – Theodor Zoulias
      2 days ago



















    0














    Since the compiler is not that smart, we must outsmart him.



    var foo = new List<int> { 1, 2, 3, 4, 5 };
    
var bar = new HashSet<int>() { 1, 3, 5 };
    
foo.RemoveAll(i => bar.Contains(i));





    share|improve this answer



















    • 1





      A hash set of 3 entries will surely not perform better, it would arguably (I have not measured) perform worse.

      – Sefe
      2 days ago






    • 3





      @Sefe While there is probably a difference between the hash set and the array, I think the point of this answer was to create bar outside of the anonymous function so that's it's created only once and to avoid the creation overhead.

      – Joshua Taylor
      2 days ago






    • 2





      @Sefe what you say is true, but I think that the OP provided a trivial example just to illustrate a point. In a real world scenario the lists will be probably longer than that.

      – Theodor Zoulias
      2 days ago














    Your Answer






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    3 Answers
    3






    active

    oldest

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    3 Answers
    3






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    13














    The answer is no it doesn't optimize out the allocation of the array



    Basically, every time the predicate is called, it checks against the compiler generated class and initializes a new array to call the Contains (as you can see here)



    private sealed class <>c
    
{
    
    public static readonly <>c <>9 = new <>c();
    

    
    public static Predicate<int> <>9__0_0;
    

    
    internal bool <M>b__0_0(int i)
    
    {
    
        // bam!
    
        int obj = new int[3];
    
        RuntimeHelpers.InitializeArray(obj, (RuntimeFieldHandle)/*OpCode not supported: LdMemberToken*/);
    
        return Enumerable.Contains(obj, i);
    
    }
    
}





    share|improve this answer






























      13














      The answer is no it doesn't optimize out the allocation of the array



      Basically, every time the predicate is called, it checks against the compiler generated class and initializes a new array to call the Contains (as you can see here)



      private sealed class <>c
      
{
      
    public static readonly <>c <>9 = new <>c();
      

      
    public static Predicate<int> <>9__0_0;
      

      
    internal bool <M>b__0_0(int i)
      
    {
      
        // bam!
      
        int obj = new int[3];
      
        RuntimeHelpers.InitializeArray(obj, (RuntimeFieldHandle)/*OpCode not supported: LdMemberToken*/);
      
        return Enumerable.Contains(obj, i);
      
    }
      
}





      share|improve this answer




























        13












        13








        13







        The answer is no it doesn't optimize out the allocation of the array



        Basically, every time the predicate is called, it checks against the compiler generated class and initializes a new array to call the Contains (as you can see here)



        private sealed class <>c
        
{
        
    public static readonly <>c <>9 = new <>c();
        

        
    public static Predicate<int> <>9__0_0;
        

        
    internal bool <M>b__0_0(int i)
        
    {
        
        // bam!
        
        int obj = new int[3];
        
        RuntimeHelpers.InitializeArray(obj, (RuntimeFieldHandle)/*OpCode not supported: LdMemberToken*/);
        
        return Enumerable.Contains(obj, i);
        
    }
        
}





        share|improve this answer















        The answer is no it doesn't optimize out the allocation of the array



        Basically, every time the predicate is called, it checks against the compiler generated class and initializes a new array to call the Contains (as you can see here)



        private sealed class <>c
        
{
        
    public static readonly <>c <>9 = new <>c();
        

        
    public static Predicate<int> <>9__0_0;
        

        
    internal bool <M>b__0_0(int i)
        
    {
        
        // bam!
        
        int obj = new int[3];
        
        RuntimeHelpers.InitializeArray(obj, (RuntimeFieldHandle)/*OpCode not supported: LdMemberToken*/);
        
        return Enumerable.Contains(obj, i);
        
    }
        
}






        share|improve this answer














        share|improve this answer



        share|improve this answer








        edited 2 days ago









        kara

        2,20031126




        2,20031126










        answered 2 days ago









        Michael RandallMichael Randall

        37.2k84171




        37.2k84171

























            4














            As @Michael Randall already wrote, it looks like it is not possible.



            I agree, that your questioned code is nicely readable, having the list in the RemoveAll method. But to have the instance only once, I have three ideas of doing it:



            int a = null;
            
foo.RemoveAll(i => (a ?? (a = new { 1, 3, 5 })).Contains(i));


            This is actually yours, with little un-beatuness of needing an external variable.



             foo = foo.Except(new { 1, 3, 5 }).ToList();


            That's actually pretty nice solution using Linq.



             new List<int>{1, 3, 5}.ForEach(x => foo.Remove(x));
            

            

            
 new {1, 3, 5}.Iterate(x => foo.Remove(x));


            This is something I'd do. In neary all of my code I have my Extension method "Iterate" to avoid the need of foreach. And also, i dont want to "toList" everything all the time to make a .ForEach(..)



            static class Extensions
            
{
            
    public static void Iterate<TSource>(this IEnumerable<TSource> source, Action<TSource> action)
            
    {
            
        foreach (var item in source)
            
        {
            
            action.Invoke(item);
            
        }
            
    }
            
}





            share|improve this answer



















            • 5





              Beware, RemoveAll performs vastly better that multiple calls to Remove.

              – Theodor Zoulias
              2 days ago
















            4














            As @Michael Randall already wrote, it looks like it is not possible.



            I agree, that your questioned code is nicely readable, having the list in the RemoveAll method. But to have the instance only once, I have three ideas of doing it:



            int a = null;
            
foo.RemoveAll(i => (a ?? (a = new { 1, 3, 5 })).Contains(i));


            This is actually yours, with little un-beatuness of needing an external variable.



             foo = foo.Except(new { 1, 3, 5 }).ToList();


            That's actually pretty nice solution using Linq.



             new List<int>{1, 3, 5}.ForEach(x => foo.Remove(x));
            

            

            
 new {1, 3, 5}.Iterate(x => foo.Remove(x));


            This is something I'd do. In neary all of my code I have my Extension method "Iterate" to avoid the need of foreach. And also, i dont want to "toList" everything all the time to make a .ForEach(..)



            static class Extensions
            
{
            
    public static void Iterate<TSource>(this IEnumerable<TSource> source, Action<TSource> action)
            
    {
            
        foreach (var item in source)
            
        {
            
            action.Invoke(item);
            
        }
            
    }
            
}





            share|improve this answer



















            • 5





              Beware, RemoveAll performs vastly better that multiple calls to Remove.

              – Theodor Zoulias
              2 days ago














            4












            4








            4







            As @Michael Randall already wrote, it looks like it is not possible.



            I agree, that your questioned code is nicely readable, having the list in the RemoveAll method. But to have the instance only once, I have three ideas of doing it:



            int a = null;
            
foo.RemoveAll(i => (a ?? (a = new { 1, 3, 5 })).Contains(i));


            This is actually yours, with little un-beatuness of needing an external variable.



             foo = foo.Except(new { 1, 3, 5 }).ToList();


            That's actually pretty nice solution using Linq.



             new List<int>{1, 3, 5}.ForEach(x => foo.Remove(x));
            

            

            
 new {1, 3, 5}.Iterate(x => foo.Remove(x));


            This is something I'd do. In neary all of my code I have my Extension method "Iterate" to avoid the need of foreach. And also, i dont want to "toList" everything all the time to make a .ForEach(..)



            static class Extensions
            
{
            
    public static void Iterate<TSource>(this IEnumerable<TSource> source, Action<TSource> action)
            
    {
            
        foreach (var item in source)
            
        {
            
            action.Invoke(item);
            
        }
            
    }
            
}





            share|improve this answer













            As @Michael Randall already wrote, it looks like it is not possible.



            I agree, that your questioned code is nicely readable, having the list in the RemoveAll method. But to have the instance only once, I have three ideas of doing it:



            int a = null;
            
foo.RemoveAll(i => (a ?? (a = new { 1, 3, 5 })).Contains(i));


            This is actually yours, with little un-beatuness of needing an external variable.



             foo = foo.Except(new { 1, 3, 5 }).ToList();


            That's actually pretty nice solution using Linq.



             new List<int>{1, 3, 5}.ForEach(x => foo.Remove(x));
            

            

            
 new {1, 3, 5}.Iterate(x => foo.Remove(x));


            This is something I'd do. In neary all of my code I have my Extension method "Iterate" to avoid the need of foreach. And also, i dont want to "toList" everything all the time to make a .ForEach(..)



            static class Extensions
            
{
            
    public static void Iterate<TSource>(this IEnumerable<TSource> source, Action<TSource> action)
            
    {
            
        foreach (var item in source)
            
        {
            
            action.Invoke(item);
            
        }
            
    }
            
}






            share|improve this answer












            share|improve this answer



            share|improve this answer










            answered 2 days ago









            MaliorMalior

            798311




            798311








            • 5





              Beware, RemoveAll performs vastly better that multiple calls to Remove.

              – Theodor Zoulias
              2 days ago














            • 5





              Beware, RemoveAll performs vastly better that multiple calls to Remove.

              – Theodor Zoulias
              2 days ago








            5




            5





            Beware, RemoveAll performs vastly better that multiple calls to Remove.

            – Theodor Zoulias
            2 days ago





            Beware, RemoveAll performs vastly better that multiple calls to Remove.

            – Theodor Zoulias
            2 days ago











            0














            Since the compiler is not that smart, we must outsmart him.



            var foo = new List<int> { 1, 2, 3, 4, 5 };
            
var bar = new HashSet<int>() { 1, 3, 5 };
            
foo.RemoveAll(i => bar.Contains(i));





            share|improve this answer



















            • 1





              A hash set of 3 entries will surely not perform better, it would arguably (I have not measured) perform worse.

              – Sefe
              2 days ago






            • 3





              @Sefe While there is probably a difference between the hash set and the array, I think the point of this answer was to create bar outside of the anonymous function so that's it's created only once and to avoid the creation overhead.

              – Joshua Taylor
              2 days ago






            • 2





              @Sefe what you say is true, but I think that the OP provided a trivial example just to illustrate a point. In a real world scenario the lists will be probably longer than that.

              – Theodor Zoulias
              2 days ago


















            0














            Since the compiler is not that smart, we must outsmart him.



            var foo = new List<int> { 1, 2, 3, 4, 5 };
            
var bar = new HashSet<int>() { 1, 3, 5 };
            
foo.RemoveAll(i => bar.Contains(i));





            share|improve this answer



















            • 1





              A hash set of 3 entries will surely not perform better, it would arguably (I have not measured) perform worse.

              – Sefe
              2 days ago






            • 3





              @Sefe While there is probably a difference between the hash set and the array, I think the point of this answer was to create bar outside of the anonymous function so that's it's created only once and to avoid the creation overhead.

              – Joshua Taylor
              2 days ago






            • 2





              @Sefe what you say is true, but I think that the OP provided a trivial example just to illustrate a point. In a real world scenario the lists will be probably longer than that.

              – Theodor Zoulias
              2 days ago
















            0












            0








            0







            Since the compiler is not that smart, we must outsmart him.



            var foo = new List<int> { 1, 2, 3, 4, 5 };
            
var bar = new HashSet<int>() { 1, 3, 5 };
            
foo.RemoveAll(i => bar.Contains(i));





            share|improve this answer













            Since the compiler is not that smart, we must outsmart him.



            var foo = new List<int> { 1, 2, 3, 4, 5 };
            
var bar = new HashSet<int>() { 1, 3, 5 };
            
foo.RemoveAll(i => bar.Contains(i));






            share|improve this answer












            share|improve this answer



            share|improve this answer










            answered 2 days ago









            Theodor ZouliasTheodor Zoulias

            19719




            19719








            • 1





              A hash set of 3 entries will surely not perform better, it would arguably (I have not measured) perform worse.

              – Sefe
              2 days ago






            • 3





              @Sefe While there is probably a difference between the hash set and the array, I think the point of this answer was to create bar outside of the anonymous function so that's it's created only once and to avoid the creation overhead.

              – Joshua Taylor
              2 days ago






            • 2





              @Sefe what you say is true, but I think that the OP provided a trivial example just to illustrate a point. In a real world scenario the lists will be probably longer than that.

              – Theodor Zoulias
              2 days ago
















            • 1





              A hash set of 3 entries will surely not perform better, it would arguably (I have not measured) perform worse.

              – Sefe
              2 days ago






            • 3





              @Sefe While there is probably a difference between the hash set and the array, I think the point of this answer was to create bar outside of the anonymous function so that's it's created only once and to avoid the creation overhead.

              – Joshua Taylor
              2 days ago






            • 2





              @Sefe what you say is true, but I think that the OP provided a trivial example just to illustrate a point. In a real world scenario the lists will be probably longer than that.

              – Theodor Zoulias
              2 days ago










            1




            1





            A hash set of 3 entries will surely not perform better, it would arguably (I have not measured) perform worse.

            – Sefe
            2 days ago





            A hash set of 3 entries will surely not perform better, it would arguably (I have not measured) perform worse.

            – Sefe
            2 days ago




            3




            3





            @Sefe While there is probably a difference between the hash set and the array, I think the point of this answer was to create bar outside of the anonymous function so that's it's created only once and to avoid the creation overhead.

            – Joshua Taylor
            2 days ago





            @Sefe While there is probably a difference between the hash set and the array, I think the point of this answer was to create bar outside of the anonymous function so that's it's created only once and to avoid the creation overhead.

            – Joshua Taylor
            2 days ago




            2




            2





            @Sefe what you say is true, but I think that the OP provided a trivial example just to illustrate a point. In a real world scenario the lists will be probably longer than that.

            – Theodor Zoulias
            2 days ago







            @Sefe what you say is true, but I think that the OP provided a trivial example just to illustrate a point. In a real world scenario the lists will be probably longer than that.

            – Theodor Zoulias
            2 days ago




















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            數位音樂下載 為非以「實體」方式來販賣音樂的相關產品，而使用數位格式如mp3、AAC等文件格式來進行銷售販賣的一种音乐产业形式。著名的數位音樂下載服務商有iTunes Store、RecoChoku、Google Play音乐和微软Zune等。数字音乐下载在二十一世纪初一度风靡全球， [1] [2] 使得传统唱片产业走向衰落，但其自身也在2010年代流媒体音乐服务如Apple Music、Spotify等的挤压下迅速失去市场份额。 [3] [4] 数字音乐下载有便于携带、传播迅速、制作简单成本低等优点，与流媒体音乐相比也能更好保障音乐人权益； [5] 但它同时很可能带来侵犯版权和滥用的情形， [6] 也给音乐产业带来了诸多不利影响。数字音乐下载为音乐人和乐迷提供了更加便捷直接的交流渠道，也一定程度上推动了网络音乐人的出现和独立音乐的迅速发展。 [7] 目录 1 历史 1.1 技术积淀（1987-2000） 1.2 出现与兴起（2000-2004） 1.3 唱片市场的颠覆者（2004-2007） 1.4 巅峰和衰落（2005-2013） 1.5 摇摇欲坠的现状与不可预知的明天（2014至今） 2 主要文件格式 2.1 PCM编码格式 2.1.1 WAV 2.1.2 APE 2.1.3 FLAC 2.2 苹果推出的无损文件格式 2.2.1 AIFF 2.2.2 ALAC 2.3 有损压缩格式 2.3.1 MP3 2.3.2 AAC 3 主要市场 3.1 iTunes Store 3.2 Google Play音乐商店 3.3 亚马逊音乐商店 3.4 部分其他音乐商店 4 影响与评价 4.1 对音乐产业的影响 4.2 对科技行业的影响 4.3 正面评价 4.4 负面评价 4.4.1 侵权问题 4.4.2 经营模式不明晰 4.4.3 不适应移动时代 4.5 文化现象 5 延伸阅读 6 参考资料 历史 苹果iTunes+iPod的软硬件搭配让数字音
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            格利澤436b

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            格利泽436b 太陽系外行星 太陽系外行星列表 艺术家笔下的格利泽436b 母恆星 母恆星 Gliese 436 星座 獅子座 赤經 ( α ) 11 h  42 m  11.0941 s [1] 赤緯 ( δ ) +26° 42′ 23.652″ [1] 距離 33.4 ly (10.2 pc) 光譜類型 M2.5 V [1] 軌道參數 半长轴 ( a ) 0.0291±0.0004 [2] AU 軌道離心率 ( e ) 0.150±0.012 [2] 公轉週期 ( P ) 2.643904±0.000005 [3] d (0.00723849 y) 軌道傾角 ( i ) 85.8 +0.21 −0.25 [3] ° 角距 ( θ ) 2.794 mas 近星點時間 ( T 0 ) 2,451,551.716 ±0.01 JD 半振幅 ( K ) 18.68±0.8 m/s 物理性质 质量 ( m ) 22.2±1.0 [2] M ⊕ 半徑 ( r ) 4.327±0.183 [2] [4] R ⊕ 密度 ( ρ ) 1.51 g cm -3 表面重力 ( g ) 1.18 g 溫度 ( T ) 712±36 [2] K 發現 發現時間 2004 發現者 巴特勒、沃格特、 馬西 et al. 發現方法 徑向速度、凌日法 發現地點 美國加利福尼亞州 發表論文 出版 其他名稱 Ross 905 b, GJ 436 b, [5] LTT 13213 b, GCTP 2704.10 b, LHS 310, AC+27:28217 b, Vyssotsky 616 b, HIP 57087 b, GEN# +9.80120068 b, LP 319-75 b, G 121-7 b, LSPM J1142+2642 b, 1RXS J114211.9+264328 b, ASCC 683818 b, G 147-68 b, UCAC2 41198281 b, BP
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            When can things happen in Etherscan, such as the picture below?

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            2 I don't know why balance of the address is 0. when can this situation? etherscan balances share | improve this question asked yesterday Ru Hi Ru Hi 11 1 New contributor Ru Hi is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct. add a comment  | 
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