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November 27, 2012
type determination
How can I make something like the following work without "Error: 
cannot append type double to type string[]" ?


T[] some_function(T[] var) {
 T[] var2;
 double a = 12.34;
 string b = "hello";

 if(typeof(var).stringof == "double") {
   var2 ~= a;
 }
 if(typeof(var).stringof == "string") {
   var2 ~= b;
 }

...
}
November 27, 2012
Re: type determination
On 11/26/2012 09:03 PM, dsmith wrote:
> How can I make something like the following work without "Error: cannot
> append type double to type string[]" ?
>
>
> T[] some_function(T[] var) {
> T[] var2;
> double a = 12.34;
> string b = "hello";
>
> if(typeof(var).stringof == "double") {
> var2 ~= a;
> }
> if(typeof(var).stringof == "string") {
> var2 ~= b;
> }
>
> ...
> }
>
>

One way is to dispatch the selection to a "traits" template:

template valueToAdd(T : double)
{
    T valueToAdd = 12.34;
}

template valueToAdd(T : string)
{
    T valueToAdd = "hello";
}


T[] some_function(T)(T[] var) {
    T[] var2;
    var2 ~= valueToAdd!T;
    return var2;
}

import std.stdio;

void main()
{
    writeln(some_function([ 1.25, 2.75 ]));
    writeln(some_function([ "abc", "xyz" ]));
}

Ali
November 27, 2012
Re: type determination
On 2012-11-27 06:03, dsmith wrote:
> How can I make something like the following work without "Error: cannot
> append type double to type string[]" ?
>
>
> T[] some_function(T[] var) {
>   T[] var2;
>   double a = 12.34;
>   string b = "hello";
>
>   if(typeof(var).stringof == "double") {
>     var2 ~= a;
>   }
>   if(typeof(var).stringof == "string") {
>     var2 ~= b;
>   }
>
> ...
> }

Use static-if, but you shouldn't use .stringof. Check the actual type 
and not the string of the type:

static if(is(typeof(var) == double)) {
    var2 ~= a;
}

static if(is(typeof(var) == string)) {
    var2 ~= b;
}

-- 
/Jacob Carlborg
November 27, 2012
Re: type determination
On Tuesday, 27 November 2012 at 07:28:34 UTC, Jacob Carlborg 
wrote:
> On 2012-11-27 06:03, dsmith wrote:
>> How can I make something like the following work without 
>> "Error: cannot
>> append type double to type string[]" ?
>>
>>
>> T[] some_function(T[] var) {
>>  T[] var2;
>>  double a = 12.34;
>>  string b = "hello";
>>
>>  if(typeof(var).stringof == "double") {
>>    var2 ~= a;
>>  }
>>  if(typeof(var).stringof == "string") {
>>    var2 ~= b;
>>  }
>>
>> ...
>> }
>
> Use static-if, but you shouldn't use .stringof. Check the 
> actual type and not the string of the type:
>
> static if(is(typeof(var) == double)) {
>     var2 ~= a;
> }
>
> static if(is(typeof(var) == string)) {
>     var2 ~= b;
> }

Oh, the "static if" ... for compile time evaluation; seems 
unintuitive (no?) since data is encountered at run time.
November 27, 2012
Re: type determination
On Tuesday, November 27, 2012 11:30:31 dsmith wrote:
> Oh, the "static if" ... for compile time evaluation; seems
> unintuitive (no?) since data is encountered at run time.

But the types are known at compile time. If you're doing anything with types, 
it has to be done at compile time.

- Jonathan M Davis
November 27, 2012
Re: type determination
On Tuesday, 27 November 2012 at 10:45:19 UTC, Jonathan M Davis 
wrote:
> On Tuesday, November 27, 2012 11:30:31 dsmith wrote:
>> Oh, the "static if" ... for compile time evaluation; seems
>> unintuitive (no?) since data is encountered at run time.
>
> But the types are known at compile time. If you're doing 
> anything with types,
> it has to be done at compile time.
>
> - Jonathan M Davis

Indeed, based on the parameter in the function call.
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