Type int? vs type int












29















I've this comparison which equals false as expected



bool eq = typeof(int?).Equals(typeof(int));


now I have this code



List<object> items = new List<object>() { (int?)123 };

int result = items.OfType<int>().FirstOrDefault();


but this returns 123 - anyway that value is of type int?



How can this be?






c# casting







share|improve this question























  • int? boxed as int , and basically every Nullable type, Edit : Marc Gravell have the full answer

    – styx
    2 days ago













  • Related post about nullable type: stackoverflow.com/questions/4028830/…. This is called as "type lifting".

    – Tetsuya Yamamoto
    2 days ago











  • Before reading this topic I wouldn't even guess that even List<int?> already holds just int types. Proof

    – Sinatr
    2 days ago






  • 7





    @Sinatr no, that is incorrect; List<int?> holds int?. The important distinction in this example is the use of List<object>. What you're seeing in that "proof" is something very different; GetType() on any T? either returns the T, or throws a NRE. It never returns T? - better example: dotnetfiddle.net/3Gy3Fa - and as for why: because GetType() is non-virtual, it cannot be overridden, and thus calling GetType() is a boxing operation (even if used via "constrained call"). And when you box a T?, you either get a T as an object, or a null.

    – Marc Gravell♦
    2 days ago













  • @TetsuyaYamamoto That is not a relevant link. How is the boxing/unboxing behavior of Nullable<T> possible? is.

    – GSerg
    2 days ago
















29















I've this comparison which equals false as expected



bool eq = typeof(int?).Equals(typeof(int));


now I have this code



List<object> items = new List<object>() { (int?)123 };

int result = items.OfType<int>().FirstOrDefault();


but this returns 123 - anyway that value is of type int?



How can this be?






c# casting







share|improve this question























  • int? boxed as int , and basically every Nullable type, Edit : Marc Gravell have the full answer

    – styx
    2 days ago













  • Related post about nullable type: stackoverflow.com/questions/4028830/…. This is called as "type lifting".

    – Tetsuya Yamamoto
    2 days ago











  • Before reading this topic I wouldn't even guess that even List<int?> already holds just int types. Proof

    – Sinatr
    2 days ago






  • 7





    @Sinatr no, that is incorrect; List<int?> holds int?. The important distinction in this example is the use of List<object>. What you're seeing in that "proof" is something very different; GetType() on any T? either returns the T, or throws a NRE. It never returns T? - better example: dotnetfiddle.net/3Gy3Fa - and as for why: because GetType() is non-virtual, it cannot be overridden, and thus calling GetType() is a boxing operation (even if used via "constrained call"). And when you box a T?, you either get a T as an object, or a null.

    – Marc Gravell♦
    2 days ago













  • @TetsuyaYamamoto That is not a relevant link. How is the boxing/unboxing behavior of Nullable<T> possible? is.

    – GSerg
    2 days ago














29












29








29


4






I've this comparison which equals false as expected



bool eq = typeof(int?).Equals(typeof(int));


now I have this code



List<object> items = new List<object>() { (int?)123 };

int result = items.OfType<int>().FirstOrDefault();


but this returns 123 - anyway that value is of type int?



How can this be?






c# casting







share|improve this question














I've this comparison which equals false as expected



bool eq = typeof(int?).Equals(typeof(int));


now I have this code



List<object> items = new List<object>() { (int?)123 };

int result = items.OfType<int>().FirstOrDefault();


but this returns 123 - anyway that value is of type int?



How can this be?






c# casting




c# casting






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 2 days ago









Dr. SnailDr. Snail

718728




718728













  • int? boxed as int , and basically every Nullable type, Edit : Marc Gravell have the full answer

    – styx
    2 days ago













  • Related post about nullable type: stackoverflow.com/questions/4028830/…. This is called as "type lifting".

    – Tetsuya Yamamoto
    2 days ago











  • Before reading this topic I wouldn't even guess that even List<int?> already holds just int types. Proof

    – Sinatr
    2 days ago






  • 7





    @Sinatr no, that is incorrect; List<int?> holds int?. The important distinction in this example is the use of List<object>. What you're seeing in that "proof" is something very different; GetType() on any T? either returns the T, or throws a NRE. It never returns T? - better example: dotnetfiddle.net/3Gy3Fa - and as for why: because GetType() is non-virtual, it cannot be overridden, and thus calling GetType() is a boxing operation (even if used via "constrained call"). And when you box a T?, you either get a T as an object, or a null.

    – Marc Gravell♦
    2 days ago













  • @TetsuyaYamamoto That is not a relevant link. How is the boxing/unboxing behavior of Nullable<T> possible? is.

    – GSerg
    2 days ago



















  • int? boxed as int , and basically every Nullable type, Edit : Marc Gravell have the full answer

    – styx
    2 days ago













  • Related post about nullable type: stackoverflow.com/questions/4028830/…. This is called as "type lifting".

    – Tetsuya Yamamoto
    2 days ago











  • Before reading this topic I wouldn't even guess that even List<int?> already holds just int types. Proof

    – Sinatr
    2 days ago






  • 7





    @Sinatr no, that is incorrect; List<int?> holds int?. The important distinction in this example is the use of List<object>. What you're seeing in that "proof" is something very different; GetType() on any T? either returns the T, or throws a NRE. It never returns T? - better example: dotnetfiddle.net/3Gy3Fa - and as for why: because GetType() is non-virtual, it cannot be overridden, and thus calling GetType() is a boxing operation (even if used via "constrained call"). And when you box a T?, you either get a T as an object, or a null.

    – Marc Gravell♦
    2 days ago













  • @TetsuyaYamamoto That is not a relevant link. How is the boxing/unboxing behavior of Nullable<T> possible? is.

    – GSerg
    2 days ago

















int? boxed as int , and basically every Nullable type, Edit : Marc Gravell have the full answer

– styx
2 days ago







int? boxed as int , and basically every Nullable type, Edit : Marc Gravell have the full answer

– styx
2 days ago















Related post about nullable type: stackoverflow.com/questions/4028830/…. This is called as "type lifting".

– Tetsuya Yamamoto
2 days ago





Related post about nullable type: stackoverflow.com/questions/4028830/…. This is called as "type lifting".

– Tetsuya Yamamoto
2 days ago













Before reading this topic I wouldn't even guess that even List<int?> already holds just int types. Proof

– Sinatr
2 days ago





Before reading this topic I wouldn't even guess that even List<int?> already holds just int types. Proof

– Sinatr
2 days ago




7




7





@Sinatr no, that is incorrect; List<int?> holds int?. The important distinction in this example is the use of List<object>. What you're seeing in that "proof" is something very different; GetType() on any T? either returns the T, or throws a NRE. It never returns T? - better example: dotnetfiddle.net/3Gy3Fa - and as for why: because GetType() is non-virtual, it cannot be overridden, and thus calling GetType() is a boxing operation (even if used via "constrained call"). And when you box a T?, you either get a T as an object, or a null.

– Marc Gravell♦
2 days ago







@Sinatr no, that is incorrect; List<int?> holds int?. The important distinction in this example is the use of List<object>. What you're seeing in that "proof" is something very different; GetType() on any T? either returns the T, or throws a NRE. It never returns T? - better example: dotnetfiddle.net/3Gy3Fa - and as for why: because GetType() is non-virtual, it cannot be overridden, and thus calling GetType() is a boxing operation (even if used via "constrained call"). And when you box a T?, you either get a T as an object, or a null.

– Marc Gravell♦
2 days ago















@TetsuyaYamamoto That is not a relevant link. How is the boxing/unboxing behavior of Nullable<T> possible? is.

– GSerg
2 days ago





@TetsuyaYamamoto That is not a relevant link. How is the boxing/unboxing behavior of Nullable<T> possible? is.

– GSerg
2 days ago












2 Answers
2






active

oldest

votes


















42














Nullable types have special "boxing" rules; "boxing" is when a value-type is treated as object, as per your code. Unlike regular value-types, a nullable value-type is boxed either as null (regular null, no type), or as the non-nullable type (the T in T?). So: an int? is boxed as an int, not an int?. Then when you use OfType<int>() on it, you get all the values that are int, which is: the single value you passed in, since it is of type int.






share|improve this answer
























  • phew ok thank you for that explanaion. Is that C# basic knowledge?

    – Dr. Snail
    2 days ago






  • 12





    @Dr.Snail "basic" is relative / subjective, and I'd wager that a good percentage of developers never have a need to know that nuance; it is useful context if you're dealing with boxing, though... and technically it isn't really C# knowledge, but rather: .NET knowledge (it would apply to all languages)

    – Marc Gravell♦
    2 days ago








  • 4





    @Sinatr you can't - the list never contains int? - it only contains int because of the boxing rules on nullable types

    – Marc Gravell♦
    2 days ago








  • 1





    @KyleJohnson you added a nullable int to the list. Naively, if nullable ints and ints are different things, you'd expect asking for all the ints in the list to return nothing. There are languages that do it that way, but C# has chosen to do it differently.

    – mbrig
    2 days ago






  • 1





    (and yes, my first sentence there is technically wrong. The nullable int never got added to the list. But if you don't know what's happening here, that's what it looks like is happening)

    – mbrig
    2 days ago



















5














A nullable value type is boxed by the following rules:




  • If HasValue returns false, the null reference is produced.

  • If HasValue returns true, a value of the underlying value type T is
    boxed, not the instance of nullable.



In your example second rule has been followed as you have value, e.g.
var i = (object)(int?)123;






share|improve this answer


























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    2 Answers
    2






    active

    oldest

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    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    42














    Nullable types have special "boxing" rules; "boxing" is when a value-type is treated as object, as per your code. Unlike regular value-types, a nullable value-type is boxed either as null (regular null, no type), or as the non-nullable type (the T in T?). So: an int? is boxed as an int, not an int?. Then when you use OfType<int>() on it, you get all the values that are int, which is: the single value you passed in, since it is of type int.






    share|improve this answer
























    • phew ok thank you for that explanaion. Is that C# basic knowledge?

      – Dr. Snail
      2 days ago






    • 12





      @Dr.Snail "basic" is relative / subjective, and I'd wager that a good percentage of developers never have a need to know that nuance; it is useful context if you're dealing with boxing, though... and technically it isn't really C# knowledge, but rather: .NET knowledge (it would apply to all languages)

      – Marc Gravell♦
      2 days ago








    • 4





      @Sinatr you can't - the list never contains int? - it only contains int because of the boxing rules on nullable types

      – Marc Gravell♦
      2 days ago








    • 1





      @KyleJohnson you added a nullable int to the list. Naively, if nullable ints and ints are different things, you'd expect asking for all the ints in the list to return nothing. There are languages that do it that way, but C# has chosen to do it differently.

      – mbrig
      2 days ago






    • 1





      (and yes, my first sentence there is technically wrong. The nullable int never got added to the list. But if you don't know what's happening here, that's what it looks like is happening)

      – mbrig
      2 days ago
















    42














    Nullable types have special "boxing" rules; "boxing" is when a value-type is treated as object, as per your code. Unlike regular value-types, a nullable value-type is boxed either as null (regular null, no type), or as the non-nullable type (the T in T?). So: an int? is boxed as an int, not an int?. Then when you use OfType<int>() on it, you get all the values that are int, which is: the single value you passed in, since it is of type int.






    share|improve this answer
























    • phew ok thank you for that explanaion. Is that C# basic knowledge?

      – Dr. Snail
      2 days ago






    • 12





      @Dr.Snail "basic" is relative / subjective, and I'd wager that a good percentage of developers never have a need to know that nuance; it is useful context if you're dealing with boxing, though... and technically it isn't really C# knowledge, but rather: .NET knowledge (it would apply to all languages)

      – Marc Gravell♦
      2 days ago








    • 4





      @Sinatr you can't - the list never contains int? - it only contains int because of the boxing rules on nullable types

      – Marc Gravell♦
      2 days ago








    • 1





      @KyleJohnson you added a nullable int to the list. Naively, if nullable ints and ints are different things, you'd expect asking for all the ints in the list to return nothing. There are languages that do it that way, but C# has chosen to do it differently.

      – mbrig
      2 days ago






    • 1





      (and yes, my first sentence there is technically wrong. The nullable int never got added to the list. But if you don't know what's happening here, that's what it looks like is happening)

      – mbrig
      2 days ago














    42












    42








    42







    Nullable types have special "boxing" rules; "boxing" is when a value-type is treated as object, as per your code. Unlike regular value-types, a nullable value-type is boxed either as null (regular null, no type), or as the non-nullable type (the T in T?). So: an int? is boxed as an int, not an int?. Then when you use OfType<int>() on it, you get all the values that are int, which is: the single value you passed in, since it is of type int.






    share|improve this answer













    Nullable types have special "boxing" rules; "boxing" is when a value-type is treated as object, as per your code. Unlike regular value-types, a nullable value-type is boxed either as null (regular null, no type), or as the non-nullable type (the T in T?). So: an int? is boxed as an int, not an int?. Then when you use OfType<int>() on it, you get all the values that are int, which is: the single value you passed in, since it is of type int.







    share|improve this answer












    share|improve this answer



    share|improve this answer










    answered 2 days ago









    Marc Gravell♦Marc Gravell

    792k19821592561




    792k19821592561













    • phew ok thank you for that explanaion. Is that C# basic knowledge?

      – Dr. Snail
      2 days ago






    • 12





      @Dr.Snail "basic" is relative / subjective, and I'd wager that a good percentage of developers never have a need to know that nuance; it is useful context if you're dealing with boxing, though... and technically it isn't really C# knowledge, but rather: .NET knowledge (it would apply to all languages)

      – Marc Gravell♦
      2 days ago








    • 4





      @Sinatr you can't - the list never contains int? - it only contains int because of the boxing rules on nullable types

      – Marc Gravell♦
      2 days ago








    • 1





      @KyleJohnson you added a nullable int to the list. Naively, if nullable ints and ints are different things, you'd expect asking for all the ints in the list to return nothing. There are languages that do it that way, but C# has chosen to do it differently.

      – mbrig
      2 days ago






    • 1





      (and yes, my first sentence there is technically wrong. The nullable int never got added to the list. But if you don't know what's happening here, that's what it looks like is happening)

      – mbrig
      2 days ago



















    • phew ok thank you for that explanaion. Is that C# basic knowledge?

      – Dr. Snail
      2 days ago






    • 12





      @Dr.Snail "basic" is relative / subjective, and I'd wager that a good percentage of developers never have a need to know that nuance; it is useful context if you're dealing with boxing, though... and technically it isn't really C# knowledge, but rather: .NET knowledge (it would apply to all languages)

      – Marc Gravell♦
      2 days ago








    • 4





      @Sinatr you can't - the list never contains int? - it only contains int because of the boxing rules on nullable types

      – Marc Gravell♦
      2 days ago








    • 1





      @KyleJohnson you added a nullable int to the list. Naively, if nullable ints and ints are different things, you'd expect asking for all the ints in the list to return nothing. There are languages that do it that way, but C# has chosen to do it differently.

      – mbrig
      2 days ago






    • 1





      (and yes, my first sentence there is technically wrong. The nullable int never got added to the list. But if you don't know what's happening here, that's what it looks like is happening)

      – mbrig
      2 days ago

















    phew ok thank you for that explanaion. Is that C# basic knowledge?

    – Dr. Snail
    2 days ago





    phew ok thank you for that explanaion. Is that C# basic knowledge?

    – Dr. Snail
    2 days ago




    12




    12





    @Dr.Snail "basic" is relative / subjective, and I'd wager that a good percentage of developers never have a need to know that nuance; it is useful context if you're dealing with boxing, though... and technically it isn't really C# knowledge, but rather: .NET knowledge (it would apply to all languages)

    – Marc Gravell♦
    2 days ago







    @Dr.Snail "basic" is relative / subjective, and I'd wager that a good percentage of developers never have a need to know that nuance; it is useful context if you're dealing with boxing, though... and technically it isn't really C# knowledge, but rather: .NET knowledge (it would apply to all languages)

    – Marc Gravell♦
    2 days ago






    4




    4





    @Sinatr you can't - the list never contains int? - it only contains int because of the boxing rules on nullable types

    – Marc Gravell♦
    2 days ago







    @Sinatr you can't - the list never contains int? - it only contains int because of the boxing rules on nullable types

    – Marc Gravell♦
    2 days ago






    1




    1





    @KyleJohnson you added a nullable int to the list. Naively, if nullable ints and ints are different things, you'd expect asking for all the ints in the list to return nothing. There are languages that do it that way, but C# has chosen to do it differently.

    – mbrig
    2 days ago





    @KyleJohnson you added a nullable int to the list. Naively, if nullable ints and ints are different things, you'd expect asking for all the ints in the list to return nothing. There are languages that do it that way, but C# has chosen to do it differently.

    – mbrig
    2 days ago




    1




    1





    (and yes, my first sentence there is technically wrong. The nullable int never got added to the list. But if you don't know what's happening here, that's what it looks like is happening)

    – mbrig
    2 days ago





    (and yes, my first sentence there is technically wrong. The nullable int never got added to the list. But if you don't know what's happening here, that's what it looks like is happening)

    – mbrig
    2 days ago













    5














    A nullable value type is boxed by the following rules:




    • If HasValue returns false, the null reference is produced.

    • If HasValue returns true, a value of the underlying value type T is
      boxed, not the instance of nullable.



    In your example second rule has been followed as you have value, e.g.
    var i = (object)(int?)123;






    share|improve this answer






























      5














      A nullable value type is boxed by the following rules:




      • If HasValue returns false, the null reference is produced.

      • If HasValue returns true, a value of the underlying value type T is
        boxed, not the instance of nullable.



      In your example second rule has been followed as you have value, e.g.
      var i = (object)(int?)123;






      share|improve this answer




























        5












        5








        5







        A nullable value type is boxed by the following rules:




        • If HasValue returns false, the null reference is produced.

        • If HasValue returns true, a value of the underlying value type T is
          boxed, not the instance of nullable.



        In your example second rule has been followed as you have value, e.g.
        var i = (object)(int?)123;






        share|improve this answer















        A nullable value type is boxed by the following rules:




        • If HasValue returns false, the null reference is produced.

        • If HasValue returns true, a value of the underlying value type T is
          boxed, not the instance of nullable.



        In your example second rule has been followed as you have value, e.g.
        var i = (object)(int?)123;







        share|improve this answer














        share|improve this answer



        share|improve this answer








        edited 2 days ago

























        answered 2 days ago









        JohnnyJohnny

        3,5551021




        3,5551021






























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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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            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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            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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