[API Proposal]: InterpolatedStringHandler allow method overload that has the "name" of the interpolated values.

[LokiMidgard]

Background and motivation

In some casese it may be of relevance to know from where the value was recived.

E.g.: A structual logger may want to know the variable to use when logging.

API Proposal

public void AppendFormatted<T> (T value, int alignment, string? format, string name);

name will contain the text wiritten in source code.

API Usage

subject = "Mail";
logger.LogInformation($"Create entity {subject}");

will call public void AppendFormatted<T> (T value, int alignment, string? format, string name); with
T: string
value:: "Mail"
alignment: 0
format: null
name: "subject"

Alternative Designs

public void AppendFormatted<T> (T value, int alignment, string? format, System.Linq.Expression name);

An alternateive, or additon could be to use Expressions to get more information.

Risks

Besides an increased complexexty I currently see no risk.
I can't anticipate the performance costs if Expressiontrees are used, but for the string variant I don't expect a high cost.

[HaloFour]

You can use CallerArgumentExpressionAttribute to achieve this with a custom interpolated string handler:

public void AppendFormatted<T> (
    T value,
    int alignment,
    string? format,
    [CallerArgumentExpression("value")] string? name = null) { ... }

[HaloFour]

Note that this will contain the expression used within the interpolation hole. If that's just a variable name, it will be that variable name, but if it's a more complicated expression, it will be that whole expression, e.g. "x + y" or "name.ToUpper()".

[LokiMidgard]

Perfect, I wasn't aware that I could just add CallerArgument stuff.

Thank you :)