computedGoto pragma
The computedGoto pragma can be used to tell the compiler how to compile a Nim case in a while true statement. Syntactically it has to be used as a statement inside the loop:
type
MyEnum = enum
enumA, enumB, enumC, enumD, enumE
proc vm() =
var instructions: array[0..100, MyEnum]
instructions[2] = enumC
instructions[3] = enumD
instructions[4] = enumA
instructions[5] = enumD
instructions[6] = enumC
instructions[7] = enumA
instructions[8] = enumB
instructions[12] = enumE
var pc = 0
while true:
{.computedGoto.}
let instr = instructions[pc]
case instr
of enumA:
echo "yeah A"
of enumC, enumD:
echo "yeah CD"
of enumB:
echo "yeah B"
of enumE:
break
inc(pc)
vm()
As the example shows, computedGoto is mostly useful for interpreters. If the underlying backend (C compiler) does not support the computed goto extension the pragma is simply ignored.
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