Re: Template mixins and struct constructors
On Wednesday, 2 March 2016 at 20:39:57 UTC, Adam D. Ruppe wrote: On Wednesday, 2 March 2016 at 12:27:04 UTC, Adrian Matoga wrote: Is it by design or is it a bug? And, if it is by design, what is the reason for that? That's by design. It allows you to override names from a template mixin like inheritance but no runtime cost. Read my tip of the week here to see how it works and how you can combine ctors from a mixin: http://arsdnet.net/this-week-in-d/2016-feb-07.html Ah, I was on vacation at that time so that's why I don't remember reading it. :) Thanks! It's a nice workaround but it's, well, a workaround. It leaks the internals of the template mixin and a potential API user would have to remember two additional quirks when using it. I guess I'll try a different approach, initializing the mixed in members later with a function.
Re: Template mixins and struct constructors
Dne 2.3.2016 v 21:39 Adam D. Ruppe via Digitalmars-d-learn napsal(a): On Wednesday, 2 March 2016 at 12:27:04 UTC, Adrian Matoga wrote: Is it by design or is it a bug? And, if it is by design, what is the reason for that? That's by design. It allows you to override names from a template mixin like inheritance but no runtime cost. Read my tip of the week here to see how it works and how you can combine ctors from a mixin: http://arsdnet.net/this-week-in-d/2016-feb-07.html I know it :). I need to upgrade my memory. I spent all day looking for it in D cookbook, because I was sure it was you who make this tip somewhere.
Re: Template mixins and struct constructors
On Wednesday, 2 March 2016 at 12:27:04 UTC, Adrian Matoga wrote: Is it by design or is it a bug? And, if it is by design, what is the reason for that? That's by design. It allows you to override names from a template mixin like inheritance but no runtime cost. Read my tip of the week here to see how it works and how you can combine ctors from a mixin: http://arsdnet.net/this-week-in-d/2016-feb-07.html
Re: Template mixins and struct constructors
On Wednesday, 2 March 2016 at 14:50:15 UTC, Adrian Matoga wrote:
On Wednesday, 2 March 2016 at 14:36:59 UTC, Daniel Kozak wrote:
OK maybe this one:
template AddField(T) {
T b;
this(Args...)(T b, auto ref Args args)
{
this.b = b;
this(args);
}
this(int a) {
this.a = a;
}
}
struct Bar {
int a;
mixin AddField!(string);
}
unittest {
auto bar1 = Bar(5);
auto bar2 = Bar("bar", 15);
}
Then it's limited to structs in which only "int a" is to be
initialized. Not very useful and the templated ctor is not
needed now.
struct Baz {
mixin AddField!string; // fail, no "int a" in Baz.
ulong d;
double x;
string foo;
}
OK then:
mixin template AddField(T) {
T b;
auto ref constructor(Args...)(T b, auto ref Args args)
{
typeof(this) r;
r.b = b;
r.__ctor(args);
return r;
}
}
struct Bar {
mixin AddField!string;
int a;
this(int a) { this.a = a; }
alias __ctor = constructor;
}
unittest {
import std.stdio;
auto bar1 = Bar(5);
auto bar2 = Bar("bar", 15);
writeln(bar1);
writeln(bar2);
}
Re: Template mixins and struct constructors
On Wednesday, 2 March 2016 at 14:36:59 UTC, Daniel Kozak wrote:
OK maybe this one:
template AddField(T) {
T b;
this(Args...)(T b, auto ref Args args)
{
this.b = b;
this(args);
}
this(int a) {
this.a = a;
}
}
struct Bar {
int a;
mixin AddField!(string);
}
unittest {
auto bar1 = Bar(5);
auto bar2 = Bar("bar", 15);
}
Then it's limited to structs in which only "int a" is to be
initialized. Not very useful and the templated ctor is not needed
now.
struct Baz {
mixin AddField!string; // fail, no "int a" in Baz.
ulong d;
double x;
string foo;
}
Re: Template mixins and struct constructors
On Wednesday, 2 March 2016 at 13:18:23 UTC, Adrian Matoga wrote:
On Wednesday, 2 March 2016 at 12:48:47 UTC, Daniel Kozak wrote:
On Wednesday, 2 March 2016 at 12:27:04 UTC, Adrian Matoga
wrote:
(...)
You can use string mixins:
template AddField(T) {
enum AddField = T.stringof ~ ` b;
this(Args...)(` ~ T.stringof ~ ` b, auto ref Args args)
{
this.b = b;
this(args);
}`;
}
struct Bar {
mixin(AddField!string);
int a;
this(int a) { this.a = a; }
}
unittest {
auto bar1 = Bar(5);
auto bar2 = Bar("bar", 15); // line 31
}
What if T is private type in some other module or, even worse,
a Voldemort type?
OK maybe this one:
template AddField(T) {
T b;
this(Args...)(T b, auto ref Args args)
{
this.b = b;
this(args);
}
this(int a) {
this.a = a;
}
}
struct Bar {
int a;
mixin AddField!(string);
}
unittest {
auto bar1 = Bar(5);
auto bar2 = Bar("bar", 15);
}
Re: Template mixins and struct constructors
On Wednesday, 2 March 2016 at 12:48:47 UTC, Daniel Kozak wrote:
On Wednesday, 2 March 2016 at 12:27:04 UTC, Adrian Matoga wrote:
(...)
You can use string mixins:
template AddField(T) {
enum AddField = T.stringof ~ ` b;
this(Args...)(` ~ T.stringof ~ ` b, auto ref Args args)
{
this.b = b;
this(args);
}`;
}
struct Bar {
mixin(AddField!string);
int a;
this(int a) { this.a = a; }
}
unittest {
auto bar1 = Bar(5);
auto bar2 = Bar("bar", 15); // line 31
}
What if T is private type in some other module or, even worse, a
Voldemort type?
Re: Template mixins and struct constructors
On Wednesday, 2 March 2016 at 12:27:04 UTC, Adrian Matoga wrote:
I can do this:
struct Foo {
int a;
string b;
this(int a) { this.a = a; }
this(Args...)(string b, auto ref Args args) { this.b = b;
this(args); }
}
unittest {
auto foo1 = Foo(5);
auto foo2 = Foo("foo", 15);
}
However, the following code is invalid:
mixin template AddField(T) {
T b;
this(Args...)(T b, auto ref Args args)
{
this.b = b;
this(args);
}
}
struct Bar {
mixin AddField!string;
int a;
this(int a) { this.a = a; }
}
unittest {
auto bar1 = Bar(5);
auto bar2 = Bar("bar", 15); // line 31
}
sctor.d(31): Error: constructor sctor.Bar.this (int a) is not
callable using argument types (string, int)
Is it by design or is it a bug?
And, if it is by design, what is the reason for that?
I would say it is by design. What this will generate is something
like:
struct Bar {
static struct _scope {
string b;
this(Args...)(string b, auto ref Args args) {
this.b = b; this(args);
}
}
int a;
this(int a) { this.a = a; }
}
Re: Template mixins and struct constructors
On Wednesday, 2 March 2016 at 12:27:04 UTC, Adrian Matoga wrote:
I can do this:
struct Foo {
int a;
string b;
this(int a) { this.a = a; }
this(Args...)(string b, auto ref Args args) { this.b = b;
this(args); }
}
unittest {
auto foo1 = Foo(5);
auto foo2 = Foo("foo", 15);
}
However, the following code is invalid:
mixin template AddField(T) {
T b;
this(Args...)(T b, auto ref Args args)
{
this.b = b;
this(args);
}
}
struct Bar {
mixin AddField!string;
int a;
this(int a) { this.a = a; }
}
unittest {
auto bar1 = Bar(5);
auto bar2 = Bar("bar", 15); // line 31
}
sctor.d(31): Error: constructor sctor.Bar.this (int a) is not
callable using argument types (string, int)
Is it by design or is it a bug?
And, if it is by design, what is the reason for that?
You can use string mixins:
template AddField(T) {
enum AddField = T.stringof ~ ` b;
this(Args...)(` ~ T.stringof ~ ` b, auto ref Args args)
{
this.b = b;
this(args);
}`;
}
struct Bar {
mixin(AddField!string);
int a;
this(int a) { this.a = a; }
}
unittest {
auto bar1 = Bar(5);
auto bar2 = Bar("bar", 15); // line 31
}
Template mixins and struct constructors
I can do this:
struct Foo {
int a;
string b;
this(int a) { this.a = a; }
this(Args...)(string b, auto ref Args args) { this.b = b;
this(args); }
}
unittest {
auto foo1 = Foo(5);
auto foo2 = Foo("foo", 15);
}
However, the following code is invalid:
mixin template AddField(T) {
T b;
this(Args...)(T b, auto ref Args args)
{
this.b = b;
this(args);
}
}
struct Bar {
mixin AddField!string;
int a;
this(int a) { this.a = a; }
}
unittest {
auto bar1 = Bar(5);
auto bar2 = Bar("bar", 15); // line 31
}
sctor.d(31): Error: constructor sctor.Bar.this (int a) is not
callable using argument types (string, int)
Is it by design or is it a bug?
And, if it is by design, what is the reason for that?
