www.digitalmars.com         C & C++   DMDScript  

D - let the implementation be the definition

reply Lewis <dethbomb hotmail.com> writes:
admittedly, im green around the gills when it comes to a language such as D,
but 
i have a complaint/question/suggestion...

Why must functions and such be declared twice?

It is my understanding that the predeclared function is to serve as a prototype 
for the compiler to do type checking and make sure that the calling is correct. 
I dont understand why this is needed as the actual function itself could easily 
serve as the prototype for itself, IMHO.

Could someone be kind enough to explain why this is needed? and why it isnt 
possible to make the function implemtation also its declaration.
Jan 03 2004
parent reply "Walter" <walter digitalmars.com> writes:
"Lewis" <dethbomb hotmail.com> wrote in message
news:bt5t92$2dr1$1 digitaldaemon.com...

 admittedly, im green around the gills when it comes to a language such as


D, but

 i have a complaint/question/suggestion...

 Why must functions and such be declared twice?


Why indeed. They don't in D <g>.


 It is my understanding that the predeclared function is to serve as a


prototype

 for the compiler to do type checking and make sure that the calling is


correct.

 I dont understand why this is needed as the actual function itself could


easily

 serve as the prototype for itself, IMHO.

 Could someone be kind enough to explain why this is needed? and why it


isnt

 possible to make the function implemtation also its declaration.


It's needed in C and C++ because the semantics of the language are
compile-as-you-go one pass through the file. That design was appropriate for
machines with little memory. D, on the other hand, does multiple passes over
the code, so forward declarations are not needed. Machines have much more
memory now, so the old compromises are unnecessary.

Ironically, compiling C++ these days requires a great deal of memory, even
though it remains a one pass semantic language.
Jan 03 2004
parent reply Lewis <dethbomb hotmail.com> writes:
Walter wrote:

 "Lewis" <dethbomb hotmail.com> wrote in message
 news:bt5t92$2dr1$1 digitaldaemon.com...
 

admittedly, im green around the gills when it comes to a language such as


 
 D, but
 

i have a complaint/question/suggestion...

Why must functions and such be declared twice?


 
 
 Why indeed. They don't in D <g>.
 
 

It is my understanding that the predeclared function is to serve as a


 
 prototype
 

for the compiler to do type checking and make sure that the calling is


 
 correct.
 

I dont understand why this is needed as the actual function itself could


 
 easily
 

serve as the prototype for itself, IMHO.

Could someone be kind enough to explain why this is needed? and why it


 
 isnt
 

possible to make the function implemtation also its declaration.


 
 
 It's needed in C and C++ because the semantics of the language are
 compile-as-you-go one pass through the file. That design was appropriate for
 machines with little memory. D, on the other hand, does multiple passes over
 the code, so forward declarations are not needed. Machines have much more
 memory now, so the old compromises are unnecessary.
 
 Ironically, compiling C++ these days requires a great deal of memory, even
 though it remains a one pass semantic language.
 
 


thanks for the reply walter

i guess im at a loss *still* when it comes to how 'import' works...
it is my belief that when i type import std.c.string; that all the functions 
within that file should then be available in the current module as if i had 
pasted the code into that module (i think)

Ive spent two weeks messing with things trying to figure out how to make 
functions i have in another module work in the current module, it keeps giving 
me a undeclared error as in:
Error 42: Symbol Undefined _Left 12  //a Left() function i coded in another
module
Ive added all my modules to the command line, imported all modules, and every 
other thing i can think of and it still wont recognize when i use a function 
from another module in my current module. -sigh

If someone is willing to help i could paste some code that im using from each 
module and to help me get the command line i need to make it compile...

frustrated newbie :)
Lewis
Jan 07 2004
next sibling parent reply Andy Friesen <andy ikagames.com> writes:
Lewis wrote:

 i guess im at a loss *still* when it comes to how 'import' works...
 it is my belief that when i type import std.c.string; that all the 
 functions within that file should then be available in the current 
 module as if i had pasted the code into that module (i think)
 
 Ive spent two weeks messing with things trying to figure out how to make 
 functions i have in another module work in the current module, it keeps 
 giving me a undeclared error as in:
 Error 42: Symbol Undefined _Left 12  //a Left() function i coded in 
 another module
 Ive added all my modules to the command line, imported all modules, and 
 every other thing i can think of and it still wont recognize when i use 
 a function from another module in my current module. -sigh
 
 If someone is willing to help i could paste some code that im using from 
 each module and to help me get the command line i need to make it 
 compile...
 
 frustrated newbie :)
 Lewis


a.d:
     import b;

     int main()
     {
         B();

         return 0;
     }

b.d:
     void B() {
         printf("B!\n");
     }

Then, at the command line:
     D:\temp\dstuff>dmd a.d b.d

     D:\temp\dstuff>a
     B!


  -- andy
Jan 07 2004
parent reply Lewis <dethbomb hotmail.com> writes:
Andy Friesen wrote:


 Lewis wrote:
 

 i guess im at a loss *still* when it comes to how 'import' works...
 it is my belief that when i type import std.c.string; that all the 
 functions within that file should then be available in the current 
 module as if i had pasted the code into that module (i think)

 Ive spent two weeks messing with things trying to figure out how to 
 make functions i have in another module work in the current module, it 
 keeps giving me a undeclared error as in:
 Error 42: Symbol Undefined _Left 12  //a Left() function i coded in 
 another module
 Ive added all my modules to the command line, imported all modules, 
 and every other thing i can think of and it still wont recognize when 
 i use a function from another module in my current module. -sigh

 If someone is willing to help i could paste some code that im using 
 from each module and to help me get the command line i need to make it 
 compile...

 frustrated newbie :)
 Lewis


 
 
 a.d:
     import b;
 
     int main()
     {
         B();
 
         return 0;
     }
 
 b.d:
     void B() {
         printf("B!\n");
     }
 
 Then, at the command line:
     D:\temp\dstuff>dmd a.d b.d
 
     D:\temp\dstuff>a
     B!
 
 
  -- andy


thanks andy,
that seems to be what im doing (similar to what someone else mentioned before), 
i must be not including the modules correctly in my commandline somewhere...
off 
to try again :)

regards
Lewis
Jan 07 2004
parent J Anderson <REMOVEanderson badmama.com.au> writes:
inline

Lewis wrote:


 Andy Friesen wrote:


 Lewis wrote:


 i guess im at a loss *still* when it comes to how 'import' works...
 it is my belief that when i type import std.c.string; that all the 
 functions within that file should then be available in the current 
 module as if i had pasted the code into that module (i think)

 Ive spent two weeks messing with things trying to figure out how to 
 make functions i have in another module work in the current module, 
 it keeps giving me a undeclared error as in:
 Error 42: Symbol Undefined _Left 12  //a Left() function i coded in 
 another module
 Ive added all my modules to the command line, imported all modules, 
 and every other thing i can think of and it still wont recognize 
 when i use a function from another module in my current module. -sigh

 If someone is willing to help i could paste some code that im using 
 from each module and to help me get the command line i need to make 
 it compile...

 frustrated newbie :)
 Lewis




 a.d:
     import b;

     int main()
     {
         B();

         return 0;
     }

 b.d:
     void B() {
         printf("B!\n");
     }

 Then, at the command line:
     D:\temp\dstuff>dmd a.d b.d

     D:\temp\dstuff>a
     B!


  -- andy



 thanks andy,
 that seems to be what im doing (similar to what someone else mentioned 
 before), i must be not including the modules correctly in my 
 commandline somewhere... off to try again :)

 regards
 Lewis


If you haven't solved the problem (and for other problems), it would be 
helpful if you sent an example, with either you make file or the command 
line entry your using.  That way we'll be able to solve your problem 
much more quickly.  Two weeks? You should of posted sooner <g>

Anderson
Jan 07 2004
prev sibling parent "Walter" <walter digitalmars.com> writes:
"Lewis" <dethbomb hotmail.com> wrote in message
news:bthmng$2i94$1 digitaldaemon.com...

 Error 42: Symbol Undefined _Left 12  //a Left() function i coded in


another module

That's coming from the linker. It means (most likely) that the module
defining Left() is missing from the command to the linker.
Jan 10 2004