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digitalmars.D.learn - can't access an alias created inside an if statement

reply Flade <consolemaster0 gmail.com> writes:
I have used an if-else statement to create an alias to avoid code 
duplication but it doesn't let me access it outside the if 
statement. Is there a way to solve this?
Aug 05 2020
parent reply Simen =?UTF-8?B?S2rDpnLDpXM=?= <simen.kjaras gmail.com> writes:
On Wednesday, 5 August 2020 at 09:05:36 UTC, Flade wrote:

 I have used an if-else statement to create an alias to avoid 
 code duplication but it doesn't let me access it outside the if 
 statement. Is there a way to solve this?


You're probably looking for static if:

     static if (useAlias) {
         alias myAlias = getAlias!();
     }

     myAlias foo = getFoo();


What happens is a regular if statement introduces a scope, so 
anything declared inside it is unavailable outside. static if 
does not introduce a new scope, and so its contents can be 
accessed.

static if only works with compile-time constant conditions, but 
aliases are also compile-time constructs, so this should not pose 
a problem.

--
   Simen
Aug 05 2020
parent reply Flade <consolemaster0 gmail.com> writes:
On Wednesday, 5 August 2020 at 09:25:23 UTC, Simen Kjærås wrote:

 On Wednesday, 5 August 2020 at 09:05:36 UTC, Flade wrote:

 I have used an if-else statement to create an alias to avoid 
 code duplication but it doesn't let me access it outside the 
 if statement. Is there a way to solve this?


 You're probably looking for static if:

     static if (useAlias) {
         alias myAlias = getAlias!();
     }

     myAlias foo = getFoo();


 What happens is a regular if statement introduces a scope, so 
 anything declared inside it is unavailable outside. static if 
 does not introduce a new scope, and so its contents can be 
 accessed.

 static if only works with compile-time constant conditions, but 
 aliases are also compile-time constructs, so this should not 
 pose a problem.

 --
   Simen


Thanks! You see it should work but the thing is. I'm using it 
inside a function. I'm checking for one of the function's 
parameter (if parameter == false) and it says that "the variable 
`parameter` cannot be read at compile time. Do you know if there 
is a way to fix this?
Aug 05 2020
parent reply Simen =?UTF-8?B?S2rDpnLDpXM=?= <simen.kjaras gmail.com> writes:
On Wednesday, 5 August 2020 at 09:32:58 UTC, Flade wrote:

 Thanks! You see it should work but the thing is. I'm using it 
 inside a function. I'm checking for one of the function's 
 parameter (if parameter == false) and it says that "the 
 variable `parameter` cannot be read at compile time. Do you 
 know if there is a way to fix this?


As the error message says, the value must be known at compile 
time. Most likely, you can simply pass it as a template parameter:

     void fun(bool parameter)(int arg1, string arg2) {
         static if (parameter) {
         }
     }

     void main() {
         fun!true(1, "foo");
         fun!false(19, "bar");
     }

--
   Simen
Aug 05 2020
parent Flade <consolemaster0 gmail.com> writes:
On Wednesday, 5 August 2020 at 09:39:47 UTC, Simen Kjærås wrote:

 On Wednesday, 5 August 2020 at 09:32:58 UTC, Flade wrote:

 Thanks! You see it should work but the thing is. I'm using it 
 inside a function. I'm checking for one of the function's 
 parameter (if parameter == false) and it says that "the 
 variable `parameter` cannot be read at compile time. Do you 
 know if there is a way to fix this?


 As the error message says, the value must be known at compile 
 time. Most likely, you can simply pass it as a template 
 parameter:

     void fun(bool parameter)(int arg1, string arg2) {
         static if (parameter) {
         }
     }

     void main() {
         fun!true(1, "foo");
         fun!false(19, "bar");
     }

 --
   Simen


Thanks man! Works as expected! Have a great day!
Aug 05 2020