Contributed by StitchyPie and Lorenzobattistela

BuiltinList

The primitive ListLiteral class in Mojo.

A ListLiteral is a list of elements that are immutable, it only includes getter methods for accessing elements, nothing can be modified post-initialization.

init

The types can be implicit:

let list = [1,2,3]
print(list)

[1, 2, 3]

Or explicit:

let explicit_list: ListLiteral[Int, Int, Int] = [1, 2, 3]
print(explicit_list)

[1, 2, 3]

A ListLiteral can also contain elements of different types.

let mixed_list= [1, 2.0, True]
print(mixed_list)

[1, 2.0, True]

fields

• storage: this is the MLIR type that stores the literals, we'll force an error to see what mixed_list storage looks like:

mixed_list.storage = 0

error: Expression [8]:20:26: cannot implicitly convert 'Int' value to '!pop.pack<[!kgen.declref<_"$Builtin"::_"$Int"::_Int>, !kgen.declref<_"$Builtin"::_"$FloatLiteral"::_FloatLiteral>, !kgen.declref<_"$Builtin"::_"$Bool"::_Bool>]>' in assignment
    mixed_list.storage = 0
                         ^

expression failed to parse (no further compiler diagnostics)

len

print(len(mixed_list))

3

get

Get a list element at the given index with the element type, note that we have to specify the index of the element and the type of the element we're retrieving, refer to parametrization here

print(mixed_list.get[0, Int]())
print(mixed_list.get[2, Bool]())

1
True

let x = -1
print(x.__index__())

-1