Difference between is X and is X _

Question

Before C# 7.0, the following code was valid:

if(x is X)
{
    //...
}

Now, the following is also valid:

if(x is X _)
{
    //...
}

Accoding to TryRoslyn , those code sections generates the same IL. My question is: what's the purpose of the discard operator in pattern matching, if it is not necessary neither useful? Am I missing something here?

This question is not the same as that one, since I'm asking the purpose of the discard operator (wildcard) specifically for the pattern matching ( is operator).

Answer 1

根据Neal Gafter的说法 ， 在这种情况下 ，抛弃运算符几乎没有用处，至少到目前为止是没有用的。

Answer 2

This is not useful yet. But when recursive pattern matching is introduced (hopefully in C# 8.0), it will be useful to have discards in part of the pattern.

The details are not finalized, but imagine something like is (1, (_, 3)) or possibly is X (1, Y (_, 3)) .