On Tuesday, 2 August 2022 at 12:39:41 UTC, pascal111 wrote:
On Tuesday, 2 August 2022 at 04:06:30 UTC, frame wrote:
On Monday, 1 August 2022 at 23:35:13 UTC, pascal111 wrote:
This is the definition of "filter" function, and I think it
called itself within its definition. I'm guessing how it
works?
It's a template that defines the function called "Eponymous
Templates":
https://dlang.org/spec/template.html#implicit_template_properties
A template generates code, it cannot be called, only
instantiated.
The common syntax is just a shortcut for using it. Otherwise
you would need to write `filter!(a => a > 0).filter([1, -1, 2,
0, -3])`. Like UFCS, some magic the compiler does for you.
Instantiation seems some complicated to me. I read "If a
template contains members whose name is the same as the
template identifier then these members are assumed to be
referred to in a template instantiation:" in the provided link,
but I'm still stuck. Do you have a down-to-earth example for
beginners to understand this concept?
A template is conceptually like a macro with parameters in C. An
instantiation is like the using of the macro in your C program.
The fundamental difference is, that the template is syntactically
and semantically linked to the language. In C, the preprocessor
was just a textual replacement done before the proper
compilation. This meant that there are things that you couldn't
do in the pre-processor (like `#if sizeof(int)==4`) and
(horrible) things that never should have been possible (I used to
use the C pre-processor with other languages like AutoLISP and
dBase III).
