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Class std.typecons.AutoImplement
AutoImplement
automatically implements (by default) all abstract member
functions in the class or interface Base
in specified way.
class AutoImplement(Base, alias how, alias what)
if (!is(how == class));
class AutoImplement(Interface, BaseClass, alias how, alias what)
if (is(Interface == interface) && is(BaseClass == class));
The second version of AutoImplement
automatically implements
Interface
, while deriving from BaseClass
.
Methods
Name | Description |
---|---|
factory
(classname)
|
Create instance of class specified by the fully qualified name classname. The class must either have no constructors or have a default constructor. |
opCmp
(o)
|
Compare with another Object obj. |
opEquals
(o)
|
Test whether this is equal to o .
The default implementation only compares by identity (using the is operator).
Generally, overrides for opEquals should attempt to compare objects by their contents.
|
toHash
()
|
Compute hash function for Object. |
toString
()
|
Convert Object to a human readable string. |
Methods
Name | Description |
---|---|
factory
(classname)
|
Create instance of class specified by the fully qualified name classname. The class must either have no constructors or have a default constructor. |
opCmp
(o)
|
Compare with another Object obj. |
opEquals
(o)
|
Test whether this is equal to o .
The default implementation only compares by identity (using the is operator).
Generally, overrides for opEquals should attempt to compare objects by their contents.
|
toHash
()
|
Compute hash function for Object. |
toString
()
|
Convert Object to a human readable string. |
Parameters
Name | Description |
---|---|
how | template which specifies how functions will be implemented/overridden.
Two arguments are passed to how : the type Base and an alias
to an implemented function. Then how must return an implemented
function body as a string.
The generated function body can use these keywords:
|
what | template which determines what functions should be
implemented/overridden.
An argument is passed to what : an alias to a non-final member
function in Base . Then what must return a boolean value.
Return true to indicate that the passed function should be
implemented/overridden.
--------------------
// Sees if fun returns something.
enum bool hasValue(alias fun) = !is(ReturnType!(fun) == void);
-------------------- |
Note
Generated code is inserted in the scope of std
module. Thus,
any useful functions outside std
cannot be used in the generated
code. To workaround this problem, you may import
necessary things in a
local struct, as done in the generateLogger()
template in the above
example.
BUGS
- Variadic arguments to constructors are not forwarded to super.
- Deep interface inheritance causes compile error with messages like "Error: function std.typecons.AutoImplement!(Foo).AutoImplement.bar does not override any function". [Bugzilla 2525]
- The
parent
keyword is actually a delegate to the super class' corresponding member function. [Bugzilla 2540] - Using alias template parameter in
how
and/orwhat
may cause strange compile error. Use template tuple parameter instead to workaround this problem. [Bugzilla 4217]
Example
interface PackageSupplier
{
int foo();
int bar();
}
static abstract class AbstractFallbackPackageSupplier : PackageSupplier
{
protected PackageSupplier default_, fallback;
this(PackageSupplier default_, PackageSupplier fallback)
{
this .default_ = default_;
this .fallback = fallback;
}
abstract int foo();
abstract int bar();
}
template fallback(T, alias func)
{
import std .format : format;
// for all implemented methods:
// - try default first
// - only on a failure run & return fallback
enum fallback = q{
scope (failure) return fallback.%1$s(args);
return default_.%1$s(args);
} .format(__traits(identifier, func));
}
// combines two classes and use the second one as fallback
alias FallbackPackageSupplier = AutoImplement!(AbstractFallbackPackageSupplier, fallback);
class FailingPackageSupplier : PackageSupplier
{
int foo(){ throw new Exception("failure"); }
int bar(){ return 2;}
}
class BackupPackageSupplier : PackageSupplier
{
int foo(){ return -1; }
int bar(){ return -1;}
}
auto registry = new FallbackPackageSupplier(new FailingPackageSupplier(), new BackupPackageSupplier());
writeln(registry .foo()); // -1
writeln(registry .bar()); // 2
Authors
Andrei Alexandrescu, Bartosz Milewski, Don Clugston, Shin Fujishiro, Kenji Hara
License
Copyright © 1999-2022 by the D Language Foundation | Page generated by ddox.