digitalmars.D.learn - How can I express the type '(int) => int' where it is a function or a
- Puming (62/62) Jul 15 2014 I'd like to have a Command class, where their is a name and a
- Rikki Cattermole (17/78) Jul 15 2014 Or using std.functional toDelegate you could convert the function into a...
I'd like to have a Command class, where their is a name and a
handler field:
```d
class Command
{
string name;
string delegate(string[]) handler;
}
```
this is ok, but sometimes I want the handler also accept a
function (lambdas are init to functions if no capture of outer
scope variables are present), but it can't.
So I'd like to generalize the Command to a template, the best
I've got sofar:
```d
alias string delegate(string[]) HandlerDele;
alias string function(string[]) HandlerFunc;
class Command(T) if (is (T HandlerDele) || is (T HandlerFunc))
{
immutable {
string name;
T handler;
}
this(string name, T handler)
{
this.name = name;
this.handler = handler;
}
}
void main()
{
HandlerFunc f = xs => xs[0]; // just a test
auto cmd = new Command!HandlerFunc("echo", f);
}
```
I've got several questions about this:
1. I cant ignore `HandlerFunc` when initiating cmd:
```d
auto cmd = new Command("echo", f); // Error: class
dshell.command.Command(T) if (is(T HandlerDele) || is(T
HandlerFunc)) is used as a type
```
Can DMD automatically infer the type here?
2. Is this the right way to do this?
3. I'd like a unified description of `a function pointer or a
delegate`, and from the experience of lambda, it seems the syntax
of lamdba is really useful here, if we have that, then instead of:
```d
void execute(T)(Context cxt, T handler) if (is (T HandlerFunc) ||
is (T HandlerDele))
{
//...
}
we could define a function that accepts a function/delegate like
this:
```d
void execute(T : string[] => string)(Context cxt, T handler)
{
//...
}
// in main
ctx.execute(xs => xs[0]);
Jul 15 2014
On 16/07/2014 3:50 p.m., Puming wrote:
I'd like to have a Command class, where their is a name and a handler
field:
```d
class Command
{
string name;
string delegate(string[]) handler;
}
```
this is ok, but sometimes I want the handler also accept a function
(lambdas are init to functions if no capture of outer scope variables
are present), but it can't.
So I'd like to generalize the Command to a template, the best I've got
sofar:
```d
alias string delegate(string[]) HandlerDele;
alias string function(string[]) HandlerFunc;
class Command(T) if (is (T HandlerDele) || is (T HandlerFunc))
{
immutable {
string name;
T handler;
}
this(string name, T handler)
{
this.name = name;
this.handler = handler;
}
}
void main()
{
HandlerFunc f = xs => xs[0]; // just a test
auto cmd = new Command!HandlerFunc("echo", f);
}
```
I've got several questions about this:
1. I cant ignore `HandlerFunc` when initiating cmd:
```d
auto cmd = new Command("echo", f); // Error: class
dshell.command.Command(T) if (is(T HandlerDele) || is(T HandlerFunc)) is
used as a type
```
Can DMD automatically infer the type here?
2. Is this the right way to do this?
3. I'd like a unified description of `a function pointer or a delegate`,
and from the experience of lambda, it seems the syntax of lamdba is
really useful here, if we have that, then instead of:
```d
void execute(T)(Context cxt, T handler) if (is (T HandlerFunc) || is (T
HandlerDele))
{
//...
}
we could define a function that accepts a function/delegate like this:
```d
void execute(T : string[] => string)(Context cxt, T handler)
{
//...
}
// in main
ctx.execute(xs => xs[0]);
Or using std.functional toDelegate you could convert the function into a
delegate.
class Command {
string name;
string delegate(string[]) handler;
this(string name, string delegate(string[]) handler) {
this.name = name;
this.handler = handler;
}
this(string name, string function(string[]) handler) {
import std.functional : toDelegate;
this.name = name;
this.handler = toDelegate(handler);
}
}
Just keep in mind, you can't go the opposite way.
Jul 15 2014
On Wednesday, 16 July 2014 at 04:10:13 UTC, Rikki Cattermole wrote:On 16/07/2014 3:50 p.m., Puming wrote:Thanks. I wonder if functions could implicitly convert to delegates...but toDelegate is OK. Also, after another dig into the language docs, I found:I'd like to have a Command class, where their is a name and a handler field: ```d class Command { string name; string delegate(string[]) handler; } ``` this is ok, but sometimes I want the handler also accept a function (lambdas are init to functions if no capture of outer scope variables are present), but it can't. So I'd like to generalize the Command to a template, the best I've got sofar: ```d alias string delegate(string[]) HandlerDele; alias string function(string[]) HandlerFunc; class Command(T) if (is (T HandlerDele) || is (T HandlerFunc)) { immutable { string name; T handler; } this(string name, T handler) { this.name = name; this.handler = handler; } } void main() { HandlerFunc f = xs => xs[0]; // just a test auto cmd = new Command!HandlerFunc("echo", f); } ``` I've got several questions about this: 1. I cant ignore `HandlerFunc` when initiating cmd: ```d auto cmd = new Command("echo", f); // Error: class dshell.command.Command(T) if (is(T HandlerDele) || is(T HandlerFunc)) is used as a type ``` Can DMD automatically infer the type here? 2. Is this the right way to do this? 3. I'd like a unified description of `a function pointer or a delegate`, and from the experience of lambda, it seems the syntax of lamdba is really useful here, if we have that, then instead of: ```d void execute(T)(Context cxt, T handler) if (is (T HandlerFunc) || is (T HandlerDele)) { //... } we could define a function that accepts a function/delegate like this: ```d void execute(T : string[] => string)(Context cxt, T handler) { //... } // in main ctx.execute(xs => xs[0]);Or using std.functional toDelegate you could convert the function into a delegate. class Command { string name; string delegate(string[]) handler; this(string name, string delegate(string[]) handler) { this.name = name; this.handler = handler; } this(string name, string function(string[]) handler) { import std.functional : toDelegate; this.name = name; this.handler = toDelegate(handler); } } Just keep in mind, you can't go the opposite way.The .ptr property of a delegate will return the frame pointer value as a void*.The .funcptr property of a delegate will return the function pointer value as a function type.Future directions: Function pointers and delegates may merge into a common syntax and be interchangeable with each other.Wonder how that would happen.
Jul 15 2014
"Kagamin" <spam here.lot> The compiler would generate calls to toDelegate and toFunction automatically.
Jul 16 2014