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digitalmars.D.learn - Default values in passing delegates to functions

reply Anonamoose <joshuamlewis2 gmail.com> writes:
I have a script in which I want a special case where someone can 
input something like a potential or a dispersion relation for use 
in physics simulations. I want to clean up the implementation for 
users as not every situation requires these. So I wrote a 
function with the signature

``` d
void myFunc(Function initialFunc, int timeSteps, double 
initialTime, double finalTime, int depth,
     double delegate(double, double) source = &nullSource, double 
delegate(double, double) spacialDispersion = &identitySource, 
bool userOutput = false) {...}
```
where
```d
static double nullSource(double a, double b) {
     return(0);
}
static double identitySource(double a, double b) {
     return(1.0);
}
```

Is this a good method of implementation? Or should I be doing 
this in a completely different way? I am not extremely new to D, 
however, I am new  to using some of the more unique and advanced 
features. Any help or advice is appreciated.
Jun 23
parent =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 6/23/21 9:16 AM, Anonamoose wrote:

 I have a script in which I want a special case where someone can input
 something like a potential or a dispersion relation for use in physics
 simulations. I want to clean up the implementation for users as not
 every situation requires these. So I wrote a function with the signature

 ``` d
 void myFunc(Function initialFunc, int timeSteps, double initialTime,
 double finalTime, int depth,
      double delegate(double, double) source = &nullSource, double
 delegate(double, double) spacialDispersion = &identitySource, bool
 userOutput = false) {...}
That function is expecting a 'delegate'...
 ```
 where
 ```d
 static double nullSource(double a, double b) {
      return(0);
 }
 static double identitySource(double a, double b) {
      return(1.0);
 }
 ```
But those are `function`s. (And `static` does not mean anything in D in that usage.)
 Is this a good method of implementation?
Yes, that would work if you deal with the `delegate` vs. `function` issue. For example, like using std.functional.toDelegate for the default arguments: import std.functional; // Ali's assumption; so that the code compiles. alias Function = int function(int); void myFunc(Function initialFunc, int timeSteps, double initialTime, double finalTime, int depth, double delegate(double, double) source = toDelegate(&nullSource), double delegate(double, double) spacialDispersion = toDelegate(&identitySource), bool userOutput = false) { // ... } static double nullSource(double a, double b) { return(0); } static double identitySource(double a, double b) { return(1.0); } void main() { } Another approach is to take the functions (or delegates) as `alias` template parameters: // Ali's assumption; so that the code compiles. alias Function = int function(int); void myFunc(alias source = nullSource, // Template parameters alias spacialDispersion = identitySource) // Regular function parameters: (Function initialFunc, int timeSteps, double initialTime, double finalTime, int depth, bool userOutput = false) { // ... } static double nullSource(double a, double b) { return(0); } static double identitySource(double a, double b) { return(1.0); } void main() { // In this case, I am calling it with a lambda: myFunc!((a, b) => a + b)(null, 1, 2, 3, 4); } Ali
Jun 23