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digitalmars.D.learn - Template variable not reach at compile

reply Greatsam4sure <greatsam4sure gmail.com> writes:
Sorry for the typo.  This is the problem

auto arithmetic(T, V, U)(T a,  V b,  U op){
    return mixin("a"~op~"b");
}

//call like this
arithmetic(1.5,2.5,"+");


Compiler says the variable op is not reach at compile time.  So 
how can the varible a and b be reach at compile time and op is 
not reach. I will appreciate any help. I have also use a static 
if but the same complain.  Just a newbie in D
Jul 21 2018
parent reply Mike Parker <aldacron gmail.com> writes:
On Saturday, 21 July 2018 at 12:17:54 UTC, Greatsam4sure wrote:

 Sorry for the typo.  This is the problem

 auto arithmetic(T, V, U)(T a,  V b,  U op){
    return mixin("a"~op~"b");
 }

 //call like this
 arithmetic(1.5,2.5,"+");


 Compiler says the variable op is not reach at compile time.  So 
 how can the varible a and b be reach at compile time and op is 
 not reach. I will appreciate any help. I have also use a static 
 if but the same complain.  Just a newbie in D


You aren't using a or b at compile time -- you're using the 
string literals "a" and "b", which have nothing at all to do with 
a and b. In order to get what you want, you need to make op a 
template parameter like this:

auto arithmetic(string op, T, V)(T a, V b)
{
     mixin("a"~op~"b");
}

arithmetic!("+")(1.5, 2.5);
Jul 21 2018
parent Greatsam4sure <greatsam4sure gmail.com> writes:
On Saturday, 21 July 2018 at 13:13:11 UTC, Mike Parker wrote:

 On Saturday, 21 July 2018 at 12:17:54 UTC, Greatsam4sure wrote:

 Sorry for the typo.  This is the problem

 auto arithmetic(T, V, U)(T a,  V b,  U op){
    return mixin("a"~op~"b");
 }

 //call like this
 arithmetic(1.5,2.5,"+");


 Compiler says the variable op is not reach at compile time.  
 So how can the varible a and b be reach at compile time and op 
 is not reach. I will appreciate any help. I have also use a 
 static if but the same complain.  Just a newbie in D


 You aren't using a or b at compile time -- you're using the 
 string literals "a" and "b", which have nothing at all to do 
 with a and b. In order to get what you want, you need to make 
 op a template parameter like this:

 auto arithmetic(string op, T, V)(T a, V b)
 {
     mixin("a"~op~"b");
 }

 arithmetic!("+")(1.5, 2.5);



Thanks Sir.  Really appreciate your reply it works for me. I also 
want to thank you for all your labour in the dlang ecosystem or 
foundation. I read about the dlang announce group every day. I 
will also want update to dlang this week or close it down or 
redirect to the announce group directly
Jul 21 2018