C# tuple in for loop without var keyword-CodePudding

I defined a tuples in a for loop like this (From Leetcode 1704)

for (var tuple = (i : 0, j : s.Length / 2); tuple.i < s.Length / 2 && tuple.j < s.Length; tuple.i  , tuple.j  ){...}

It worked properly.

Then I tried to explicitly define the variable type of the tuple.

This is the method I found on the Internet

for (Tuple<int, int> tuple = new Tuple<int, int>(i : 0, j : s.Length / 2); tuple.i < s.Length / 2 && tuple.j < s.Length; tuple.i  , tuple.j  )

And I got some errors

Line 7: Char 58: error CS1739: The best overload for 'Tuple' does not have a parameter named 'i' (in Solution.cs)
Line 7: Char 90: error CS1061: 'Tuple<int, int>' does not contain a definition for 'i' and no accessible extension method 'i' accepting a first argument of type 'Tuple<int, int>' could be found (are you missing a using directive or an assembly reference?) (in Solution.cs)
Line 7: Char 116: error CS1061: 'Tuple<int, int>' does not contain a definition for 'j' and no accessible extension method 'j' accepting a first argument of type 'Tuple<int, int>' could be found (are you missing a using directive or an assembly reference?) (in Solution.cs)
Line 7: Char 136: error CS1061: 'Tuple<int, int>' does not contain a definition for 'i' and no accessible extension method 'i' accepting a first argument of type 'Tuple<int, int>' could be found (are you missing a using directive or an assembly reference?) (in Solution.cs)
Line 7: Char 147: error CS1061: 'Tuple<int, int>' does not contain a definition for 'j' and no accessible extension method 'j' accepting a first argument of type 'Tuple<int, int>' could be found (are you missing a using directive or an assembly reference?) (in Solution.cs)
Line 9: Char 41: error CS1061: 'Tuple<int, int>' does not contain a definition for 'i' and no accessible extension method 'i' accepting a first argument of type 'Tuple<int, int>' could be found (are you missing a using directive or an assembly reference?) (in Solution.cs)
Line 10: Char 41: error CS1061: 'Tuple<int, int>' does not contain a definition for 'j' and no accessible extension method 'j' accepting a first argument of type 'Tuple<int, int>' could be found (are you missing a using directive or an assembly reference?) (in Solution.cs)

I want to know is it special to define a Tuple in a for loop? And how should I do it

(Of course it's clearer and easier to read with var... I just want to figure out how to do it without omitting.)

CodePudding user response：

A Tuple normally contains the properties Item1 and Item2. That's why you get the compilation errors in your 2nd example. It should look like this:

for (Tuple<int, int> tuple = new Tuple<int, int>(0, s.Length / 2);
     tuple.Item1 < s.Length / 2 && tuple.Item2 < s.Length; tuple.Item1  , tuple.Item2  ) { }

But that doesn't work because Tuples are immutable and you cannot increment the items. Tuples in C# 6 are not strongly typed, that's why Microsoft introduced the ValueTuple in C# 7, which is a mutable struct. Like this it will work:

for (ValueTuple<int, int> tuple = new ValueTuple<int, int>(0, s.Length / 2);
     tuple.Item1 < s.Length / 2 && tuple.Item2 < s.Length; tuple.Item1  , tuple.Item2  ) { }

If you just want to avoid the var keyword in your sample you could declare it like this:

for ((int i, int j) tuple = (i: 0, j: s.Length / 2); 
     tuple.i < s.Length / 2 && tuple.j < s.Length; tuple.i  , tuple.j  ) { }

CodePudding user response：

It doesn't matter where do you define the tuple. It matters how do you define it. Here is the correct definition (with items of type string and int):

Tuple<int, string> tuple = Tuple.Create<int, string>(0, "a string"); // Generic parameters are types of the elements

// Accessing the elements
int element1 = tuple.Item1;

A tuple can store up to 8 elements of different types.

CodePudding user response：

The "tuple" you defined in the loop isn't actually a System.Tuple<T1,T2>, it's in fact something different called a ValueTuple, check out this existing post for a good rundown of the differences:

What's the difference between System.ValueTuple and System.Tuple?