This module allows chains of field-access and indexing where the LHS can be nil. This simplifies code by reducing need for if-else branches around intermediate values that maybe be nil.

Note: experimental module and relies on {.experimental: "dotOperators".} Unstable API.


type Foo = ref object
  x1: string
  x2: Foo
  x3: ref int

var f: Foo
assert ?.f.x2.x1 == "" # returns default value since `f` is nil

var f2 = Foo(x1: "a")
f2.x2 = f2
assert ?.f2.x1 == "a" # same as f2.x1 (no nil LHS in this chain)
assert ?.Foo(x1: "a").x1 == "a" # can use constructor inside

# when you know a sub-expression is not nil, you can scope it as follows:
assert ?.(f2.x2.x2).x3[] == 0 # because `f` is nil


macro `?.`(a: untyped): untyped
Transforms a into an expression that can be safely evaluated even in presence of intermediate nil pointers/references, in which case a default value is produced.   Source Edit


template `.`(a: Wrapnil; b): untyped
See top-level example.   Source Edit
template `[]`[I; ](a: Wrapnil; i: I): untyped
See top-level example.   Source Edit
template `[]`(a: Wrapnil): untyped
See top-level example.   Source Edit