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

    votes








    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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            迪纳利峰 位于迪纳利国家公园和保留区的迪纳利峰（旧名麦金利峰） 最高点 海拔 20,237英尺（6,168米）   NGVD 29 . [1] [2] 相對高度 20,073英尺（6,118米） 列表 各洲最高峰列表 特独立山峰 各国最高点列表 美国最高点  排名第一 [3] 坐标 63°04′10″N 151°00′27″W  /  63.06944°N 151.00750°W  / 63.06944; -151.00750  ( Mount McKinley ) 坐标： 63°04′10″N 151°00′27″W  /  63.06944°N 151.00750°W  / 63.06944; -151.00750  ( Mount McKinley )   地理 位置   美國阿拉斯加州迪纳利自治市镇 迪纳利国家公园和保留区 山脈 阿拉斯加山脉 攀山 首次登頂 （ 英语 ： First ascent ） 1913年6月7日 哈德逊·史塔克 哈里·卡斯坦斯 沃尔特·哈珀 罗伯特·塔特姆 最簡路線 西坡路线（攀登冰川/雪） 迪纳利 （北阿萨巴斯卡语支、 英语： Denali ， / d ᵻ ˈ n ɑː l i / ，直译“高山”），1917年至2015年官方名称为 麦金利山 （另译作 麦金利峰 ， 英语： Mount McKinley ），位于阿拉斯加州东南部、阿拉斯加山脉中段，海拔6194米，是北美洲最高峰，也是美国的最高峰。它的俄语名称是 Большая Гора ， 罗马化：Bolshaya Gora ，意思是“大山”。 迪纳利山地区拥有变幻莫测的高山风、典型的北极植被以及野生动植物。这里大部分地区终年积雪，山间经常浓雾不断，雾气在皑皑白雪中缭绕弥漫时，几百米之外的景物便不可见。夏季，迪纳利山的青青山坡上鲜花盛开，紫色的杜鹃和精巧的铃状石南花随处可见。迪纳利山还是世界登山爱好者的汇集之地。每年5月到7月有数百人登山，只有一半不到的人能登顶成功。一次登山约花3个星期。 2015年8月31日，美國政府宣佈將山名由“麦金利山”改回原名“迪纳利山”。美國內政部發表聲
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            南乌拉尔铁路局

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            南乌拉尔铁路局 Южно-Уральская железная дорога 成立 1934年1月4日 国家   蘇聯（1934年—1991年）   俄羅斯（1991年—） 总部 车里雅宾斯克 隶属 俄罗斯铁路股份公司 路局代码 80 铁路里程 4,934.9公里 奖项 网址 http://yuzd.rzd.ru/ 查 论 编 南乌拉尔铁路局 （俄语： Южно-Уральская железная дорога ， 羅馬化： Yuzhno-Uralskaya zheleznaya doroga ，简称 ЮУЖД ）是俄罗斯铁路股份公司属下的铁路管理局之一，总部位于车里雅宾斯克，负责管辖俄罗斯联邦乌拉尔南部地区的铁路系统，范围包括奥伦堡州、车里雅宾斯克州、库尔干州的大部分铁路，以及萨马拉州、斯维尔德洛夫斯克州、巴什科尔托斯坦共和国的少部分铁路，并有部分铁路延伸至或穿过哈萨克斯坦境内。南乌拉尔铁路局的营业里程为4,934.9公里，与伏尔加铁路局、古比雪夫铁路局、斯维尔德洛夫斯克铁路局、西西伯利亚铁路局相邻，并与南方的哈萨克斯坦铁路连接。 外部链接 （俄文） Южно-Уральская железная дорога — филиал ОАО РЖД （俄文） 南乌拉尔铁路局管辖路线图（一） （俄文） 南乌拉尔铁路局管辖路线图（二） 查 论 编 俄罗斯铁路（集团）股份公司 十月铁路局 · 莫斯科铁路局 · 北高加索铁路局 · 高尔基铁路局 · 古比雪夫铁路局 · 北方铁路局 · 伏尔加铁路局 · 东南铁路局 · 斯维尔德洛夫斯克铁路局 · 南乌拉尔铁路局 · 西西伯利亚铁路局 · 克拉斯诺亚尔斯克铁路局 · 东西伯利亚铁路局 · 后贝加尔铁路局 · 远东铁路局 · 加里宁格勒铁路局 This page is only for reference, If you need detailed information, please check here
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