Suggestion: Make check and return from method in one line

[JohnyL]

We often write code similar to this:

private void SetList()
{
    var list = GetList();
    if (list == null) return;
}

private List<int> GetList()
{
    return null;
}

I suggest to make it more concise and make decision in one line with new keyword returnif:

private void SetList()
{
    returnif(var list = GetList()); //Exit when list is null
}

By default, it would check variable list for null. But when you know that returned value won't be null, then it could be expanded like this:

private void SetList()
{
    returnif(var list = GetList()).Count == 0; //Exit when list exists but has no items
}

[HaloFour]

With any discussion as to variable scoping and declarations that has occurred with other feature proposals this syntax would not keep list in scope after this returnif construct. Beyond that I find it would be quite confusing to have a single keyword that would be both a conditional and a terminating keyword, particularly given that more often than not return is used to return a value and there seems to be no capacity for that in your proposal. I'd rather keep this to two operations.

[JohnyL]

Well, I don't think it's impossible for the compiler to re-write this statement into two. Compiler re-writes lots of things - async, lambdas, using, delegate. This one-liner could really save some key strokes.

[HaloFour]

Indeed, the compiler can do a great many things. But whether or not it should is a completely different ballgame.

I'd say that the biggest problem with this proposal is how variables are declared. Leaking the scope out of the construct is in direct opposition to all conversations regarding inline variable declaration. See #254 or #6183.

Given that the rest of the proposal doesn't make much sense as you lose the ability to collapse the declaration/condition/termination to a single expression, and returnif on its own is certainly less clearer than a simple if and return.

[gafter]

This is already possible with #6400 which is implemented in the branch features/patterns

let List<int> list = GetList() else return;

Though, to be honest, I don't really see any problem with the original code you're hoping to "simplify".

[HaloFour]

@gafter Good point. Also:

let List<int> list = GetList() when list.Count > 0 else return;

I thought that the semi-colon before else was removed?

[gafter]

@HaloFour Yes, thanks, I've surgically removed the semicolon.

[gafter]

We are now taking language feature discussion on https://github.com/dotnet/csharplang for C# specific issues, https://github.com/dotnet/vblang for VB-specific features, and https://github.com/dotnet/csharplang for features that affect both languages.