mirror of
https://github.com/golang/go
synced 2024-11-11 23:40:22 -07:00
- modified type switches (replacement for CL 32659)
- takes into account new scoping rules DELTA=52 (21 added, 7 deleted, 24 changed) OCL=33967 CL=33982
This commit is contained in:
parent
9bf597a210
commit
9ecd30a286
@ -3272,9 +3272,9 @@ case x < 0: return -x
|
|||||||
default: return x
|
default: return x
|
||||||
}
|
}
|
||||||
|
|
||||||
switch { // missing expression means "true"
|
switch { // missing expression means "true"
|
||||||
case x < y: f1();
|
case x < y: f1();
|
||||||
case x < z: f2();
|
case x < z: f2();
|
||||||
case x == 4: f3();
|
case x == 4: f3();
|
||||||
}
|
}
|
||||||
</pre>
|
</pre>
|
||||||
@ -3283,9 +3283,8 @@ case x == 4: f3();
|
|||||||
|
|
||||||
<p>
|
<p>
|
||||||
A type switch compares types rather than values. It is otherwise similar
|
A type switch compares types rather than values. It is otherwise similar
|
||||||
to an expression switch. It is introduced by special
|
to an expression switch. It is marked by a special switch expression which
|
||||||
notation in the form of a simple declaration whose right hand side
|
has the form of a <a href="#Type_assertions">type assertion</a>
|
||||||
has the form of a type assertion (§<a href="#Type_assertions">Type assertions</a>)
|
|
||||||
using the reserved word <code>type</code> rather than an actual type.
|
using the reserved word <code>type</code> rather than an actual type.
|
||||||
Cases then match literal types against the dynamic type of the expression
|
Cases then match literal types against the dynamic type of the expression
|
||||||
in the type assertion.
|
in the type assertion.
|
||||||
@ -3293,23 +3292,30 @@ in the type assertion.
|
|||||||
|
|
||||||
<pre class="ebnf">
|
<pre class="ebnf">
|
||||||
TypeSwitchStmt = "switch" [ [ SimpleStmt ] ";" ] TypeSwitchGuard "{" { TypeCaseClause } "}" .
|
TypeSwitchStmt = "switch" [ [ SimpleStmt ] ";" ] TypeSwitchGuard "{" { TypeCaseClause } "}" .
|
||||||
TypeSwitchGuard = identifier ":=" Expression "." "(" "type" ")" .
|
TypeSwitchGuard = [ identifier ":=" ] Expression "." "(" "type" ")" .
|
||||||
TypeCaseClause = TypeSwitchCase ":" [ StatementList ] .
|
TypeCaseClause = TypeSwitchCase ":" [ StatementList ] .
|
||||||
TypeSwitchCase = "case" Type | "default" .
|
TypeSwitchCase = "case" Type | "default" .
|
||||||
</pre>
|
</pre>
|
||||||
|
|
||||||
<p>
|
<p>
|
||||||
As a special case, the type in the type switch case may be an
|
The TypeSwitchGuard may include a
|
||||||
identifier denoting the predeclared constant <code>nil</code>
|
<a href="#Short_variable_declarations">short variable declaration</a>.
|
||||||
(§<a href="#Predeclared_identifiers">Predeclared identifiers</a>).
|
When that form is used, the variable is declared in each clause.
|
||||||
If the interface value equals <code>nil</code>,
|
In clauses with a case listing exactly one type, the variable
|
||||||
only an explict <code>nil</code> case or "default"
|
has that type; otherwise, the variable has the type of the expression
|
||||||
case will execute.
|
in the TypeSwitchGuard.
|
||||||
</p>
|
</p>
|
||||||
|
|
||||||
<p>
|
<p>
|
||||||
Given a function <code>f</code>
|
The type in a case may be <code>nil</code>
|
||||||
that returns a value of interface type,
|
(§<a href="#Predeclared_identifiers">Predeclared identifiers</a>);
|
||||||
|
that case is used when the expression in the TypeSwitchGuard
|
||||||
|
is a nil interface value.
|
||||||
|
</p>
|
||||||
|
|
||||||
|
<p>
|
||||||
|
Given a function <code>f</code> that returns
|
||||||
|
a value of type <code>interface{}</code>,
|
||||||
the following type switch:
|
the following type switch:
|
||||||
</p>
|
</p>
|
||||||
|
|
||||||
@ -3318,11 +3324,13 @@ switch i := f().(type) {
|
|||||||
case nil:
|
case nil:
|
||||||
printString("f() returns nil");
|
printString("f() returns nil");
|
||||||
case int:
|
case int:
|
||||||
printInt(i); // i is an int
|
printInt(i); // i is an int
|
||||||
case float:
|
case float:
|
||||||
printFloat(i); // i is a float
|
printFloat(i); // i is a float
|
||||||
case func(int) float:
|
case func(int) float:
|
||||||
printFunction(i); // i is a function
|
printFunction(i); // i is a function
|
||||||
|
case bool, string:
|
||||||
|
printString("type is bool or string"); // i is an interface{}
|
||||||
default:
|
default:
|
||||||
printString("don't know the type");
|
printString("don't know the type");
|
||||||
}
|
}
|
||||||
@ -3337,25 +3345,31 @@ v := f();
|
|||||||
if v == nil {
|
if v == nil {
|
||||||
printString("f() returns nil");
|
printString("f() returns nil");
|
||||||
} else if i, is_int := v.(int); is_int {
|
} else if i, is_int := v.(int); is_int {
|
||||||
printInt(i); // i is an int
|
printInt(i); // i is an int
|
||||||
} else if i, is_float := v.(float); is_float {
|
} else if i, is_float := v.(float); is_float {
|
||||||
printFloat(i); // i is a float
|
printFloat(i); // i is a float
|
||||||
} else if i, is_func := v.(func(int) float); is_func {
|
} else if i, is_func := v.(func(int) float); is_func {
|
||||||
printFunction(i); // i is a function
|
printFunction(i); // i is a function
|
||||||
} else {
|
} else {
|
||||||
printString("don't know the type");
|
i1, is_bool := v.(bool);
|
||||||
|
i2, is_string := v.(string);
|
||||||
|
if is_bool || is_string {
|
||||||
|
i := v;
|
||||||
|
printString("type is bool or string"); // i is an interface{}
|
||||||
|
} else {
|
||||||
|
i := v;
|
||||||
|
printString("don't know the type"); // i is an interface{}
|
||||||
|
}
|
||||||
}
|
}
|
||||||
</pre>
|
</pre>
|
||||||
|
|
||||||
<p>
|
<p>
|
||||||
In a type switch, the guard is mandatory,
|
The type switch guard may be preceded by a simple statement, which
|
||||||
there can be only one type per "case", and
|
executes before the guard is evaluated.
|
||||||
the "fallthrough" statement is not allowed.
|
|
||||||
</p>
|
</p>
|
||||||
|
|
||||||
<p>
|
<p>
|
||||||
The type switch guard may be preceded by a simple statement, which
|
The "fallthrough" statement is not permitted in a type switch.
|
||||||
executes before the guard is evaluated.
|
|
||||||
</p>
|
</p>
|
||||||
|
|
||||||
<h3 id="For_statements">For statements</h3>
|
<h3 id="For_statements">For statements</h3>
|
||||||
|
Loading…
Reference in New Issue
Block a user