Allow "_" for empty delegates

[znakeeye]

If you search github for _ => { } you'll find 33 thousand usages. Five ugly tokens to declare an empty delegate ... You are almost inclined to introduce nullability just to allow for default.

Today's syntax

Foo(_ => { });
Bar(() => { });

void Foo(Action<string> bar) { }
void Bar(Action baz) { }

Suggestion

Foo(_);
Bar(_);

Parallel.ForEach(partition, options, CreateState, Run, _);

This syntax has several obvious benefits.

• Intuitive. Most developers have learnt the "ignore" keyword by now.
• Easier to read.
• Easier to explain. Try explaining the current syntax for a developer. "Now create an empty delegate. Parenthesis, parenthesis... uhm, arrow, uhm, brackets no braces. Hang on, I'll paste it in Teams instead." (Been there 😄)

[colejohnson66]

IMHO, () => {} is very clear - it's a delegate that does nothing. _ is widely used to mean "discard", and that's not what's happening here. Arguably, if a no-op delegate is a valid argument, the called method should take a nullable delegate and do a conditional invoke. Then you'd just pass in null.

[spydacarnage]

I could see a potential for something like Action.Empty, akin to IEnumerable<int>.Empty as a more descriptive and maybe memory saving option (depending on whether multiple instances of () => { } creates a new object each time or not?)

[HaloFour]

(depending on whether multiple instances of () => { } creates a new object each time or not?)

Each callsite results in a different allocation, but because there are no captures the compiler does emit code to allocate the delegate once and reuse it on future invocations at that callsite.

SharpLab

[spydacarnage]

So maybe a small benefit if used across multiple callsites, but only minimal.

[colejohnson66]

Action.Empty can't exist because of how delegate types are implemented. I don't know if the IL prohibits properties on delegate types, but C# certainly does.

[spydacarnage]

Fair enough. Maybe an extension member in future...