[Proposal] Conditional return statements

[LWChris]

I have come to grow very fond of the concise, unindented code block that you can put at the start of a method body for safeguards using ArgumentNullException.ThrowIfNull(arg) etc.

However, the "neatness" of these blocks is disturbed when you want to return rather than throw:

private List<Video>? _videos;
public Video? GetVideoByIndex(int index) {
    if (_videos is null) {
        return null;
    }
    ArgumentOutOfRangeException.ThrowIfNegative(index);
    ArgumentOutOfRangeException.ThrowIfGreaterThanOrEqual(index, _videos.Count);
    return _videos[index];
}

You can try to force it into a single line, like so:

public Video? GetVideoByIndex(int index) {
    if (_videos is null) return null;
    ArgumentOutOfRangeException.ThrowIfNegative(index);
    ArgumentOutOfRangeException.ThrowIfGreaterThanOrEqual(index, _videos.Count);
    return _videos[index];
}

but that wouldn't persist in any codebase I have worked on so far, since they all enforce brackets and new lines for if statements. (Maybe people would agree to have return and throw statements as an exception, but since you cannot configure that, those neat one-liners will be expanded upon next code cleanup. It gets even worse if the style also enforces an empty line after a closing }.)

Therefore, I would like to suggest conditional returns:

public Video? GetVideoByIndex(int index) {
    return null if _videos is null;
    ArgumentOutOfRangeException.ThrowIfNegative(index);
    ArgumentOutOfRangeException.ThrowIfGreaterThanOrEqual(index.Value, _videos);
    return _videos[index];
}

The part behind the if is any expression valid for an if statement, so you could also do stuff like

private int? CoerceIndex(int? index) {
    return null if index is null || _videos is null;
    return 0 if index < 0;
    return _videos.Count - 1 if index >= videos.Count;
    return index;
}

which actually yields natural English language when read aloud, and is IMHO slightly prettier than one-liners (if they persisted)

private int? CoerceIndex(int? index) {
    if (_videos is null || index is null) return null;
    if (index < 0) return 0;
    if (index >= _videos.Count) return _videos.Count - 1;
    return index;
}

and a lot more concise than

private int? CoerceIndex(int? index) {
    if (_videos is null || index is null) {
        return null;
    }
    if (index < 0) {
        return 0;
    }
    if (index >= _videos.Count) {
        return _videos.Count - 1;
    }
    return index;
}

Bonus thoughts:

1. The suggestion omits ( ) brackets for the conditional expression, since there is no code between if and ; that's not part of it.
2. I considered using when instead of if because that would look similar to catch x when y, but I think x when y means y is a filter for x, which it wouldn't be in return x when y.
3. Of coure there should also be the equivalent return if <expr>; statement for void methods.

P. S.: Since I suspect the syntax highlighting isn't going to work on my proposal, here's what the code would look like when highlighted:

[HaloFour]

See: #2195 #6345

Idiomatic C# would be:

if (condition) return expr;

[LWChris]

Okay, if you do not agree with "having all returns in front is prettier" and solely focus on the style guide issue, then yes, that's not valid for a change.

But actually, any idea how to do

_field = parameter ?? return;

That was my original starting point. But I figured making ?? RHS accept a statement when it was an expression was probably never going to be accepted, so I figured that could be written as

return if (_field = parameter) is null;

EDIT: Forget that, if ((_field = parameter) is null) return;, obviously. Can you set "return" and "throw" as an exception to the braces and new line rules anywhere?

[HaloFour]

See: #176

[LWChris]

Thanks.

[FaustVX]

I have another problem with return if is that in some case, it has an out of order meaning:

return i if i++ == 1;

In this case, it's weird that the if expression is executed before the return expression.

[LWChris]

return i if i++ == 1;

In this case, it's weird that the if expression is executed before the return expression.

I wouldn't find it weird, since it's obvious you have to evaluate the condition to determine whether to return. After all, that would've been the point of return if. But since this syntax is never coming, and from experience I'd say something discussed for so long as #176 is also not coming within the next years, we're stuck with if i++ == 1 return i; anyway, which doesn't have that issue even if you apply "only left to right can be logical".