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Final switch on default error template #1971

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Nov 9, 2017
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Final switch on default error template #1971

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8 changes: 7 additions & 1 deletion src/core/exception.d
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Original file line number Diff line number Diff line change
Expand Up @@ -312,7 +312,7 @@ unittest
*/
class SwitchError : Error
{
@safe pure nothrow this( string file = __FILE__, size_t line = __LINE__, Throwable next = null )
@safe pure nothrow @nogc this( string file = __FILE__, size_t line = __LINE__, Throwable next = null )
{
super( "No appropriate switch clause found", file, line, next );
}
Expand Down Expand Up @@ -579,6 +579,12 @@ extern (C) void onSwitchError( string file = __FILE__, size_t line = __LINE__ )
throw new SwitchError( file, line, null );
}

// Compiler lowers final switch default case to this (which is a runtime error)
void __switch_errorT()(string file = __FILE__, size_t line = __LINE__) @trusted
{
// Consider making this a compile time check.
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@jpf91 jpf91 Nov 12, 2017

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We already have that compile time check for final switch and normal switch always requires a default branch.

I guess this runtime check is only used to verify that a value is not out-of-range, probably caused by an invalid cast. Ping @andralex

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@andralex andralex Nov 12, 2017

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@jpf91 take a look at https://dpaste.dzfl.pl/a33b4b74d774

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@jpf91 jpf91 Nov 13, 2017

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Thanks. I didn't know final switch also works on non-enumeral values.

throw staticError!SwitchError(file, line, null);
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@PetarKirov PetarKirov Nov 9, 2017 •
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Keep in mind, that we may need to add a if (__ctfe) assert (0, "informative message...") branch, as I'm not sure if staticError would work in CTFE.
I prefer to leave the PR as it is for now, and cross the bridges when we come to them.

}

/**
* A callback for unicode errors in D. A $(LREF UnicodeException) will be thrown.
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8 changes: 8 additions & 0 deletions src/object.d
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Expand Up @@ -3889,6 +3889,14 @@ unittest
testSwitch!dchar;
}

// Compiler lowers final switch default case to this (which is a runtime error)
// Old implementation is in core/exception.d
void __switch_error()(string file = __FILE__, size_t line = __LINE__)
{
import core.exception : __switch_errorT;
__switch_errorT(file, line);
}

// Helper functions

private inout(TypeInfo) getElement(inout TypeInfo value) @trusted pure nothrow
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