Compile time values & implicit conditional mixin, as an alternative to tertiary operator hell and one-compile-time functions.

[Sebastiaan Koppe]

On Saturday, 16 January 2021 at 14:20:19 UTC, Paul wrote:
> On Saturday, 16 January 2021 at 04:13:12 UTC, Paul Backus wrote:
>> You can use immediately-invoked function literals to work 
>> around all of these issues:
>>
>> enum string values = () {
>>     string result = "value.x";
>>     if (L != 1) { result ~= ",value.y"; }
>>     if (L != 2) { result ~= ",value.z"; }
>>     if (L != 3) { result ~= ",value.w"; }
>>     return result;
>> }(); // call the function we just defined
>>
>> enum string kind = () {
>>     if (is(S == uint)) { return "ui"; }
>>     else if (is(S == float)) { return "f"; }
>>     else { assert(is(S == double)); return "d"; }
>> }();
>
> This seems like a workaround for defining a function, and seems 
> semantically strange to me. You're still restricted to 
> immediate local 'onelines'. Not that my issue requires 
> non-oneliners, but were my use case to have to mix/match the 
> string depending on compile time conditions, you'd have to 
> create either many almost identical function, or ones with 
> additional reoccuring conditions, instead of building a 
> variable at compile time, with conditionals occuring only once.
>
> Thanks for the suggestion nontheless, that may be more 
> organized for my current (rougly simple, I may need more 
> complexity later on) case. 🙂

you can also use CTFE. Generate the values in a normal function, 
assign it to an enum.

---
string generateValues(uint L)() {
     string result = "value.x";
     if (L != 1) { result ~= ",value.y"; }
     if (L != 2) { result ~= ",value.z"; }
     if (L != 3) { result ~= ",value.w"; }
     return result;
}

enum string values = generateValues!3();

pragma(msg, values);

void main(){};
---