Nim supports three different types of variables,
const. As with most things, multiple variables can be declared in the same section.
proc getAlphabet(): string = var accm = "" for letter in 'a'..'z': # see iterators accm.add(letter) return accm # Computed at compilation time const alphabet = getAlphabet() # Mutable variables var a = "foo" b = 0 # Works fine, initialized to 0 c: int # Immutable variables let d = "foo" e = 5 # Compile-time error, must be initialized at creation f: float # Works fine, `a` is mutable a.add("bar") b += 1 c = 3 # Compile-time error, const cannot be modified at run-time alphabet = "abc" # Compile-time error, `d` and `e` are immutable d.add("bar") e += 1
$ nim c --verbosity:2 ./variables.nim variables.nim(22, 2) Error: 'let' symbol requires an initialization f: float ^
--verbosity:2 only the error will be shown without the position cursor.
const variable’s value will be evaluated at compile-time, so if you inspect the C sources, you’ll see the following line:
STRING_LITERAL(TMP129, "abcdefghijklmnopqrstuvwxyz", 26);
The only limitation with const is that compile-time evaluation cannot interface with C because there is no compile-time foreign function interface at this time.