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Using `is` operator with value type tuples gives error

C# 7 Pattern Match with a tupleHow do you give a C# Auto-Property a default value?Direct casting vs 'as' operator?Collection was modified; enumeration operation may not executeGet int value from enum in C#How to loop through all enum values in C#?Type Checking: typeof, GetType, or is?Extension methods defined on value types cannot be used to create delegates - Why not?Overriding == operator. How to compare to null?How do I populate current class with new class values?Why `as` is giving null for nullable value types?

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18

1

I am trying to check if an object variable is (int, int) and if so I will use the casted variable so I have tried the codes below:

//this one gives the error
public void MyMethodWithIs(object val)

 if(val is (int id, int name) pair)
 
 ConsoleWriteLine($"pair.id, pair.name");
 


//This one works
public void MyMethodWithAs(object val)

 var pair = val as (int id, int name)?;
 if(pair!=null)
 
 ConsoleWriteLine($"pair.id, pair.name");
 

The MyMethodWithIs method gives the error below in the editor:

No suitable deconstruct instance or extension method was found for type

My Question

Why one works fine but the other gives an error at all? I think MyMethodWithIs more readable and suitable to use for my case but I can't use it due to giving an error.

c# valuetuple

share|improve this question

edited May 18 at 17:29

ilkerkaran

asked May 12 at 20:22

ilkerkaranilkerkaran

1,37111325

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  AFAIK value tuples don't store item name information, so there is probably no way to check if the items are id and name. I am guessing it might work without names if (val is (int, int) pair)
  
  – Slai
  May 12 at 20:31
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Slai I also tried it, but the same error appears.
  
  – ilkerkaran
  May 12 at 20:32
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  if (val is ValueTuple<int,string> pair) works though. Somewhat related: stackoverflow.com/questions/44706498/…
  
  – György Kőszeg
  May 12 at 20:39
  
  

  
  
  
  

add a comment | 

18

1

I am trying to check if an object variable is (int, int) and if so I will use the casted variable so I have tried the codes below:

//this one gives the error
public void MyMethodWithIs(object val)

 if(val is (int id, int name) pair)
 
 ConsoleWriteLine($"pair.id, pair.name");
 


//This one works
public void MyMethodWithAs(object val)

 var pair = val as (int id, int name)?;
 if(pair!=null)
 
 ConsoleWriteLine($"pair.id, pair.name");
 

The MyMethodWithIs method gives the error below in the editor:

No suitable deconstruct instance or extension method was found for type

My Question

Why one works fine but the other gives an error at all? I think MyMethodWithIs more readable and suitable to use for my case but I can't use it due to giving an error.

c# valuetuple

share|improve this question

edited May 18 at 17:29

ilkerkaran

asked May 12 at 20:22

ilkerkaranilkerkaran

1,37111325

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  AFAIK value tuples don't store item name information, so there is probably no way to check if the items are id and name. I am guessing it might work without names if (val is (int, int) pair)
  
  – Slai
  May 12 at 20:31
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Slai I also tried it, but the same error appears.
  
  – ilkerkaran
  May 12 at 20:32
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  if (val is ValueTuple<int,string> pair) works though. Somewhat related: stackoverflow.com/questions/44706498/…
  
  – György Kőszeg
  May 12 at 20:39
  
  

  
  
  
  

add a comment | 

I am trying to check if an object variable is (int, int) and if so I will use the casted variable so I have tried the codes below:

//this one gives the error
public void MyMethodWithIs(object val)

 if(val is (int id, int name) pair)
 
 ConsoleWriteLine($"pair.id, pair.name");
 


//This one works
public void MyMethodWithAs(object val)

 var pair = val as (int id, int name)?;
 if(pair!=null)
 
 ConsoleWriteLine($"pair.id, pair.name");
 

The MyMethodWithIs method gives the error below in the editor:

No suitable deconstruct instance or extension method was found for type

My Question

Why one works fine but the other gives an error at all? I think MyMethodWithIs more readable and suitable to use for my case but I can't use it due to giving an error.

c# valuetuple

share|improve this question

edited May 18 at 17:29

ilkerkaran

asked May 12 at 20:22

ilkerkaranilkerkaran

1,37111325

//this one gives the error
public void MyMethodWithIs(object val)

 if(val is (int id, int name) pair)
 
 ConsoleWriteLine($"pair.id, pair.name");
 


//This one works
public void MyMethodWithAs(object val)

 var pair = val as (int id, int name)?;
 if(pair!=null)
 
 ConsoleWriteLine($"pair.id, pair.name");
 

share|improve this question

edited May 18 at 17:29

ilkerkaran

asked May 12 at 20:22

ilkerkaranilkerkaran

1,37111325

share|improve this question

edited May 18 at 17:29

ilkerkaran

asked May 12 at 20:22

ilkerkaranilkerkaran

1,37111325

asked May 12 at 20:22

ilkerkaranilkerkaran

1,37111325

asked May 12 at 20:22

ilkerkaranilkerkaran

1,37111325

1 Answer
1

active

oldest

votes

17

Using C# 8's pattern matching capabilities, you can write this:

if (val is (int id, int name))

 Console.WriteLine($"id: id; name: name");

However this boxes id and name, which is surprising. There's a proposal to optimize this.

Below C# 8, you can write this:

if (val is ValueTuple<int, int> pair)

 Console.WriteLine($"id: pair.Item1; name: pair.Item2");

You can of course make it a bit clearer:

if (val is ValueTuple<int, int> pair)

 var (id, name) = pair;
 Console.WriteLine($"id: id; name: name");

It looks like you can also deconstruct the ValueTuple inline:

if (val is ValueTuple<int, int>(var id, var name))

 Console.WriteLine($"id: id; name: name");

... which is somewhat horrific, but appears to be legal.

I might have expected val is (int, int) pair) to work, but it seems nobody's designed this case (yet).

share|improve this answer

edited May 14 at 9:10

answered May 12 at 20:39

canton7canton7

6,74811930

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  The first code block gives the same error. The second one works but I don't want to use Item1, Item2 etc.
  
  – ilkerkaran
  May 12 at 20:45
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ilkerkaran It works in sharplab - might be new in C# 8. sharplab.io/…
  
  – canton7
  May 12 at 20:47
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ilkerkaran found another way, added to my answer
  
  – canton7
  May 12 at 20:51
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I think my editor does not let me to use c#8 yet (I think because it is preview). Your updated answer is probably the closest I can get for now.
  
  – ilkerkaran
  May 12 at 20:54
  

  
  
  
  

add a comment | 

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17

Using C# 8's pattern matching capabilities, you can write this:

if (val is (int id, int name))

 Console.WriteLine($"id: id; name: name");

However this boxes id and name, which is surprising. There's a proposal to optimize this.

Below C# 8, you can write this:

if (val is ValueTuple<int, int> pair)

 Console.WriteLine($"id: pair.Item1; name: pair.Item2");

You can of course make it a bit clearer:

if (val is ValueTuple<int, int> pair)

 var (id, name) = pair;
 Console.WriteLine($"id: id; name: name");

It looks like you can also deconstruct the ValueTuple inline:

if (val is ValueTuple<int, int>(var id, var name))

 Console.WriteLine($"id: id; name: name");

... which is somewhat horrific, but appears to be legal.

I might have expected val is (int, int) pair) to work, but it seems nobody's designed this case (yet).

share|improve this answer

edited May 14 at 9:10

answered May 12 at 20:39

canton7canton7

6,74811930

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  The first code block gives the same error. The second one works but I don't want to use Item1, Item2 etc.
  
  – ilkerkaran
  May 12 at 20:45
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ilkerkaran It works in sharplab - might be new in C# 8. sharplab.io/…
  
  – canton7
  May 12 at 20:47
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ilkerkaran found another way, added to my answer
  
  – canton7
  May 12 at 20:51
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I think my editor does not let me to use c#8 yet (I think because it is preview). Your updated answer is probably the closest I can get for now.
  
  – ilkerkaran
  May 12 at 20:54
  

  
  
  
  

add a comment | 

17

Using C# 8's pattern matching capabilities, you can write this:

if (val is (int id, int name))

 Console.WriteLine($"id: id; name: name");

However this boxes id and name, which is surprising. There's a proposal to optimize this.

Below C# 8, you can write this:

if (val is ValueTuple<int, int> pair)

 Console.WriteLine($"id: pair.Item1; name: pair.Item2");

You can of course make it a bit clearer:

if (val is ValueTuple<int, int> pair)

 var (id, name) = pair;
 Console.WriteLine($"id: id; name: name");

It looks like you can also deconstruct the ValueTuple inline:

if (val is ValueTuple<int, int>(var id, var name))

 Console.WriteLine($"id: id; name: name");

... which is somewhat horrific, but appears to be legal.

I might have expected val is (int, int) pair) to work, but it seems nobody's designed this case (yet).

share|improve this answer

edited May 14 at 9:10

answered May 12 at 20:39

canton7canton7

6,74811930

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  The first code block gives the same error. The second one works but I don't want to use Item1, Item2 etc.
  
  – ilkerkaran
  May 12 at 20:45
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ilkerkaran It works in sharplab - might be new in C# 8. sharplab.io/…
  
  – canton7
  May 12 at 20:47
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ilkerkaran found another way, added to my answer
  
  – canton7
  May 12 at 20:51
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I think my editor does not let me to use c#8 yet (I think because it is preview). Your updated answer is probably the closest I can get for now.
  
  – ilkerkaran
  May 12 at 20:54
  

  
  
  
  

add a comment | 

Using C# 8's pattern matching capabilities, you can write this:

if (val is (int id, int name))

 Console.WriteLine($"id: id; name: name");

However this boxes id and name, which is surprising. There's a proposal to optimize this.

Below C# 8, you can write this:

if (val is ValueTuple<int, int> pair)

 Console.WriteLine($"id: pair.Item1; name: pair.Item2");

You can of course make it a bit clearer:

if (val is ValueTuple<int, int> pair)

 var (id, name) = pair;
 Console.WriteLine($"id: id; name: name");

It looks like you can also deconstruct the ValueTuple inline:

if (val is ValueTuple<int, int>(var id, var name))

 Console.WriteLine($"id: id; name: name");

... which is somewhat horrific, but appears to be legal.

I might have expected val is (int, int) pair) to work, but it seems nobody's designed this case (yet).

share|improve this answer

edited May 14 at 9:10

answered May 12 at 20:39

canton7canton7

6,74811930

if (val is (int id, int name))

 Console.WriteLine($"id: id; name: name");

if (val is ValueTuple<int, int> pair)

 Console.WriteLine($"id: pair.Item1; name: pair.Item2");

if (val is ValueTuple<int, int> pair)

 var (id, name) = pair;
 Console.WriteLine($"id: id; name: name");

if (val is ValueTuple<int, int>(var id, var name))

 Console.WriteLine($"id: id; name: name");

share|improve this answer

edited May 14 at 9:10

answered May 12 at 20:39

canton7canton7

6,74811930

answered May 12 at 20:39

canton7canton7

6,74811930

answered May 12 at 20:39

canton7canton7

6,74811930