Al already noted, semantically switch-cases are evaluated from top to bottom.
With a switch statement on an enum with a large (over 100) number of cases would it make sense to replace the switch with a dictionary of closures?
That depends on your enum. As far as I checked switch on simple enum cases like:
switch value {
case .case001:
break
case .case002:
break
case .case003:
break
...
case .case100:
break
}
It is optimized into a simple multiway branching as found in C-switch statement, even in optimization level -Onone.
SwitchCaseOptimization`MyClass.switchMethod(_:):
0x100006750 <+0>: pushq %rbp
0x100006751 <+1>: movq %rsp, %rbp
0x100006754 <+4>: movb %dil, %al
0x100006757 <+7>: movb $0x0, -0x8(%rbp)
0x10000675b <+11>: movq $0x0, -0x10(%rbp)
0x100006763 <+19>: movb %al, -0x8(%rbp)
0x100006766 <+22>: movq %r13, -0x10(%rbp)
-> 0x10000676a <+26>: movzbl %al, %eax
0x10000676d <+29>: movq %rax, -0x18(%rbp)
0x100006771 <+33>: movq -0x18(%rbp), %rax
0x100006775 <+37>: leaq 0x144(%rip), %rcx ; SwitchCaseOptimization.MyClass.switchMethod(SwitchCaseOptimization.MyCases) -> () + 368
0x10000677c <+44>: movslq (%rcx,%rax,4), %rax
0x100006780 <+48>: addq %rcx, %rax
0x100006783 <+51>: jmpq *%rax
(Please be careful, too strong optimization like -O would make whole switch statement into nop, in a simplified all break example as shown above.)
I do expect this optimization would occur in
Simple enum cases, no rawValue
Enum cases with Int as rawValue, the value range is not huge
I have not tried with enums with some cases having associated values or enum cases with String as rawValue.
(Seems internal case representation is a small int even when its rawValues are String.)
So, can you show the definition of your enum?
