Custom InterpolatedStringHandler with string.Concat like overloads

[ladeak]

The compiler seems to choose a string.Concat overload to create strings with only a few parts (instead of using the DefaultInterpolatedStringHandler), as it seems to be more performant for some scenarios.

When I create a custom interpolated string handler, is there a way to tell the compiler to use a certain method (and its overloads) for similar scenarios?

[stephentoub]

When I create a custom interpolated string handler, is there a way to tell the compiler to use a certain method (and its overloads) for similar scenarios?

Can you provide an example?

[ladeak]

I create an InterpolatedStringHandler that assembles that appends URL path segments together while also taking care of using the starting or ending /-s on each segment (trimming or appending them as needed).

$"{BaseUrl}/path/entity/{Id}/type/{TypeValue}"

But I notice that when I only have a few of these segments, the performance is less attractive. I wonder how the DefaultInterpolatedStringHandler manages this situation but from the IL it looks the compiler invokes string.Concat instead.

Hence I wonder if I create a method that has a signature like string.Concat, but has my custom implementation, then is there a way to tell the compiler to use this method instead of the my InterpolatedStringHandler?

[stephentoub]

@333fred, does OverloadResolutionPriority handle this?

[333fred]

No, OverloadResolutionPriority wouldn't help with something like this. Using an interpolated string as a string is a special case, and handled specially by the compiler because it can guarantee observed semantics.

[ladeak]

So as I understand there is no direct way to achieve this. And my suspect is that some performance is lost by the ArrayPool<T> renting and return. I would do stackalloc normally to avoid this with a fixed buffer, but similar to DefaultInterpolatedStringHandler cannot really do that in a ref struct.

EDIT: I think that I could replace the stackalloc with an inline array though - that seems to be a workable solution.