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[spec/statement] Improve no case fall-through docs #4294

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Merged
merged 2 commits into from
Aug 20, 2025
Merged

[spec/statement] Improve no case fall-through docs #4294

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da845b2
[spec/statement] Improve no `case` fall-through docs
ntrel Aug 19, 2025
c5e19ae
Do list assert(0)
ntrel Aug 20, 2025
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31 changes: 21 additions & 10 deletions spec/statement.dd
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Original file line number Diff line number Diff line change
Expand Up @@ -1465,25 +1465,36 @@ $(GNAME LastExp):
$(H3 $(LNAME2 no-implicit-fallthrough, No Implicit Fall-Through))


$(P A $(GLINK ScopeStatementList) must either be empty, or be ended with
a $(GLINK ContinueStatement), $(GLINK BreakStatement),
$(GLINK ReturnStatement), $(GLINK GotoStatement), $(GLINK2 expression, ThrowExpression)
or `assert(0)` expression unless this is the last case.)
$(P A $(GLINK ScopeStatementList) must either be empty, the last one in the `switch`,
or be ended by:)

* A $(GLINK ContinueStatement), $(GLINK BreakStatement),
$(GLINK ReturnStatement), or $(GLINK GotoStatement)
* Evaluating an $(DDSUBLINK spec/expression, assert-ct, `assert(0)` expression)
* Evaluating an expression of type $(DDSUBLINK spec/type, noreturn, `noreturn`)

$(P Simple forms of the last 2 cases above can be recognized by the compiler, but not all.)

$(SPEC_RUNNABLE_EXAMPLE_FAIL
--------------
uint i;
string message;

switch (i)
{
case 1:
message ~= "one";
message = "one";
// ERROR: implicit fall-through
case 2:
// valid: the body is empty
default:
message ~= "unknown";
message = "2 or more";
// valid: no more case statements
}
--------------

$(P $(D goto case;) can be used for explicit fall-through:)
)
$(P $(D goto case;) can be used for explicit fall-through to the next
*CaseStatement*:)

$(SPEC_RUNNABLE_EXAMPLE_RUN
--------------
Expand All @@ -1493,7 +1504,7 @@ foreach (i; 1..5)
{
switch (i)
{
default: // valid: ends with 'throw'
default: // valid: ends with `noreturn` expression evaluation
throw new Exception("unknown number");

case 3: // valid: ends with 'break' (break out of the 'switch' only)
Expand All @@ -1517,7 +1528,7 @@ writeln(message);
--------------
)
$(P $(RELATIVE_LINK2 goto-statement, `goto`) also supports jumping to
a specific case or the default case statement.)
a specific case or to the default case statement.)

$(H3 $(LNAME2 string-switch, String Switch))

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