proposal: a new string litteral to embed variables in a string

[Timothee Cour]

On Tue, Nov 5, 2013 at 7:43 PM, Chris Cain <clcain at uncg.edu> wrote:

> On Wednesday, 6 November 2013 at 02:38:57 UTC, Timothee Cour wrote:
>
>> I agree. For that suggest the following syntax (independent of this
>> proposal):
>>
>> That is, support UDA for expressions.
>>
>> ----
>> void main(){
>>   import std.conv:text;
>>
>>   int var=12;
>>
>>   @("syntax=python")
>>   r{
>>     ...snip...
>>   }
>> }
>> ----
>>
>
> I'd very nearly say that this could be a library function. Imagine it like
> this:
>
> ---
> syntax!"python"(r{
> ...
> })
> ---
>
> A bit more verbose than using a UDA but the return type could be something
> like SyntaxType!"python" and you could make it so that functions only take
> SyntaxType!"python" for some compile-time checking using the type system.
> For instance, if your function requires python code then you can specify it
> in the argument. I'd also like it to be implicitly convertable to a generic
> SyntaxType that accepts everything if you just don't care what kind of
> syntax it is.
>
> As long as it's part of the standard library, then IDEs could also take
> advantage of it. Not saying that they shouldn't also support UDAs, but just
> throwing that out there as another alternative.
>


one problem with this:

r{...} is converted to a built-in tuple, and we can't return built-in
tuples from functions (only std.typecons.tuple, which has issues, eg
unnecessary copying, can't return elements by ref, etc). Note that
returning elements by ref (when needed) is crucial for use case B in the OT
(formattedRead).

On the otherhand, I also thought about using a modification of
std.typetuple.Alias that gets an extra 1st argument to indicate syntax.
It doesn't work because when there's an expression involved we get: Error:
variable a cannot be read at compile time; eg: Alias!(a+b,"foo")
and r{...} syntax is suppose to support arbitrary expressions and forward
them as builtin tuple.
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