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[spec] Improve is(Type == keyword) and Identifier docs (#3534)
* [spec] Improve is(Type == keyword) docs Describe `== TypeCtor` more precisely and add example. Remove is(i == const) example as even if `const int i;` was used it would still be false because `i` isn't a type. Add note to prefer isModule and isPackage __traits (ideally `== module` and `== package` would be deprecated as they only pass when *Type* is not a type). For Identifier form, link to non-Identifier to avoid repeating the same info. * Fix package modules link and unclosed macro * Tighten 'declared with' -> 'of' that TypeCtor * Split up type vs pattern forms & add examples Add example of type implicitly converting to match pattern. Update `Identifier ==` example and add pattern example. Fixes Issue 23730 - Clarify IsExpression `Identifier :` and `== TypeCtor` spec. * Tweak module/package note Co-authored-by: Razvan Nitu <[email protected]> * super, return and __parameters work without Identifier --------- Co-authored-by: Razvan Nitu <[email protected]>
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‎spec/expression.dd

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@@ -2748,7 +2748,8 @@ void foo()
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$(H5 $(LNAME2 is-type-equal, $(D is $(LPAREN)) $(I Type) $(D ==) $(I TypeSpecialization) $(D $(RPAREN))))
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$(P
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The condition is satisfied if $(I Type) is semantically correct and is
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If *TypeSpecialization* is a type,
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the condition is satisfied if $(I Type) is semantically correct and is
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the same type as $(I TypeSpecialization).
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)
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-------------
@@ -2764,7 +2765,6 @@ void foo()
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-------------
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$(P
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If $(I TypeSpecialization) is one of
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$(D struct)
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$(D union)
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$(D class)
@@ -2773,27 +2773,63 @@ void foo()
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$(D __vector)
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$(D function)
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$(D delegate)
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$(D const)
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$(D immutable)
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$(D inout)
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$(D shared)
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$(D module)
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$(D package)
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then the condition is satisfied if $(I Type) is one of those.
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)
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$(SPEC_RUNNABLE_EXAMPLE_COMPILE
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---
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static assert(is(Object == class));
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int i;
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static assert(!is(i == const));
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static assert(is(ModuleInfo == struct));
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---
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$(P $(DDSUBLINK
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spec/module, package-module, Package modules) are considered to be both
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)
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$(P The `module` and `package` forms are satisfied when *Type* is a symbol, not a *type*,
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unlike the other forms. The $(DDSUBLINK spec/traits, isModule, isModule)
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and $(DDSUBLINK spec/traits, isPackage, isPackage) `__traits` should be used instead.
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$(DDSUBLINK spec/module, package-module, Package modules) are considered to be both
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packages and modules.
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)
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$(P
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*TypeSpecialization* can also be one of these keywords:
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)
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$(TABLE
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$(THEAD keyword, condition)
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$(TROW `super`, `true` if *Type* is a class or interface)
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$(TROW `return`,
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$(ARGS `true` if *Type* is a function, delegate or function pointer))
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$(TROW `__parameters`,
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$(ARGS `true` if *Type* is a function, delegate or function pointer))
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)
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$(SPEC_RUNNABLE_EXAMPLE_COMPILE
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---
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class C {}
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static assert(is(C == super));
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void foo(int i);
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static assert(!is(foo == return));
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static assert(is(typeof(foo) == return));
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static assert(is(typeof(foo) == __parameters));
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---
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)
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$(P
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If *TypeSpecialization* is a $(GLINK2 type, TypeCtor) keyword
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$(D const)
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$(D immutable)
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$(D inout)
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$(D shared)
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then the condition is satisfied if *Type* is of that *TypeCtor*:
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)
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$(SPEC_RUNNABLE_EXAMPLE_COMPILE
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---
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static assert(is(const int == const));
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static assert(is(const int[] == const));
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static assert(!is(const(int)[] == const)); // head is mutable
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static assert(!is(immutable int == const));
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---
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)
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$(P $(B See also:) $(DDLINK spec/traits, Traits, Traits).)
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$(H4 $(LNAME2 is-identifier, Identifier Forms))
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$(P *Identifier* is declared to be an alias of the resulting
@@ -2846,14 +2882,12 @@ void foo()
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)
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$(P
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The condition is satisfied if $(I Type) is semantically
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If *TypeSpecialization* is a type,
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the condition is satisfied if $(I Type) is semantically
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correct and it is the same as
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or can be implicitly converted to $(I TypeSpecialization).
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$(I TypeSpecialization) is only allowed to be a $(I Type).
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The $(I Identifier) is declared to be either an alias of the
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$(I TypeSpecialization) or, if $(I TypeSpecialization) is
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dependent on $(I Identifier), the $(I TypeSpecialization) forms
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a pattern from which the type of $(I Identifier) is deduced.
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$(I Identifier) is declared to be an alias of the
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$(I TypeSpecialization).
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)
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$(SPEC_RUNNABLE_EXAMPLE_COMPILE
@@ -2868,11 +2902,22 @@ void foo()
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static assert(is(S == int));
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---
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)
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$(P
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If $(I TypeSpecialization) is a type pattern involving
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$(I Identifier), type deduction of $(I Identifier) is attempted
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based on either *Type* or a type that it implicitly converts to.
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The condition is only satisfied if the type pattern is matched.
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)
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$(SPEC_RUNNABLE_EXAMPLE_COMPILE
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---
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alias Abc = long*;
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struct S
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{
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long* i;
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alias i this; // S converts to long*
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}
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static if (is(Abc U : U*)) // Abc is matched against the pattern U*
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static if (is(S U : U*)) // S is matched against the pattern U*
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{
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U u;
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}
@@ -2889,55 +2934,46 @@ void foo()
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$(H5 $(LNAME2 is-identifier-equal, $(D is $(LPAREN)) $(I Type) $(I Identifier) $(D ==) $(I TypeSpecialization) $(D $(RPAREN))))
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$(P
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The condition is satisfied if $(I Type) is semantically
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correct and is the same as $(I TypeSpecialization).
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The $(I Identifier) is declared to be either an alias of the
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$(I TypeSpecialization) or, if $(I TypeSpecialization) is
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dependent on $(I Identifier), the $(I TypeSpecialization) forms
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a pattern from which the type of $(I Identifier) is deduced.
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If *TypeSpecialization* is a type,
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the condition is satisfied if $(I Type) is semantically correct and is
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the same type as $(I TypeSpecialization).
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$(I Identifier) is declared to be an alias of the
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$(I TypeSpecialization).
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)
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$(SPEC_RUNNABLE_EXAMPLE_COMPILE
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---
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alias Bar = short;
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const x = 5;
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static if (is(Bar T == int)) // not satisfied, short is not int
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static if (is(typeof(x) T == const int)) // satisfied, T is now defined
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alias S = T;
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static assert(!is(T)); // T is not defined
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static assert(is(T)); // T is in scope
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pragma(msg, T); // const int
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---
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)
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$(P
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If $(I TypeSpecialization) is one of
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$(D struct)
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$(D union)
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$(D class)
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$(D interface)
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$(D enum)
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$(D __vector)
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$(D function)
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$(D delegate)
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$(D const)
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$(D immutable)
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$(D inout)
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$(D shared)
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$(D module)
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$(D package)
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then the condition is satisfied if $(I Type) is one of those.
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*TypeSpecialization* can also match the following keywords:
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)
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$(TABLE
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$(THEAD keyword, condition)
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$(TROW `super`, `true` if *Type* is a class or interface)
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$(TROW `return`,
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$(ARGS `true` is *Type* is a function, delegate or function pointer))
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$(TROW `__parameters`,
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$(ARGS `true` is *Type* is a function, delegate or function pointer))
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If $(I TypeSpecialization) is a type pattern involving
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$(I Identifier), type deduction of $(I Identifier) is attempted
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based on *Type*.
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The condition is only satisfied if the type pattern is matched.
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)
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$(SPEC_RUNNABLE_EXAMPLE_COMPILE
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---
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alias Foo = long*;
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static if (is(Foo U == U*)) // Foo is matched against the pattern U*
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{
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U u;
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}
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static assert(is(U == long));
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---
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)
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$(P
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Furthermore, $(I Identifier) is set to be an alias of the type:
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If *TypeSpecialization* is a valid keyword for the
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$(RELATIVE_LINK2 is-type-equal, `is(Type == Keyword)` form),
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the condition is satisfied in the same manner.
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$(I Identifier) is set as follows:
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)
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$(TABLE_2COLS ,

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