Friendlier "ArgumentText" and "ArgumentHelp"

[rmanthorpe]

Now that D supports UDAs on parameters it would be nice to have an @ExcelArgument UDA that you could use like this:

import xlld;

@Excel(
       HelpTopic("Adds all cells in an array"),
       FunctionHelp("Adds all cells in an array")
)
double FuncAddEverything(
    @ExcelArgument(Description("Array to add"), HelpTopic("url/of/help/topic")) double[][] args
);

[atilaneves]

I can't find any documentation on actually getting a UDA from a parameter though.

[adamdruppe]

i have a little aside tucked away in my blog about it:

http://dpldocs.info/this-week-in-d/Blog.Posted_2019_02_11.html#how-to-get-uda-on-a-function-param

...which is the only written thing i'm familiar with. i know at least one other person knows how to do this but i'm not familiar with any other public link on it!

[atilaneves]

Turns out this does it:

template getParamUDAs(alias fun, size_t paramIdx)
{
    alias P = BetterParams!fun[paramIdx .. paramIdx+1];
    static if(__traits(compiles, __traits(getAttributes, P)))
        alias getParamUDAs = __traits(getAttributes, P);
    else {
        import std.meta: AliasSeq;
        alias getParamUDAs = AliasSeq!();
    }
}


import std.traits: isCallable;
template BetterParams(func...)
if (func.length == 1 && isCallable!func)
{
    import std.traits : FunctionTypeOf;
    static if (is(FunctionTypeOf!func P == __parameters))
        alias BetterParams = P;
    else
        static assert(0, "argument has no parameters");
}