identity
identity(x)
The identity function. Returns its argument.
Examples
In the Julia programming language, the identity
function simply returns its argument.
julia> identity(5)
5
julia> identity("Hello")
"Hello"
Here are some common examples of using the identity
function:

Passing a variable through unchanged:
julia> x = 10; julia> identity(x) 10
It returns the value of
x
unchanged. 
Using
identity
in a function composition:julia> f(x) = x^2; julia> g(x) = x + 1; julia> h = f ∘ g ∘ identity; julia> h(5) 36
Here,
identity
is used in a function composition to pass the intermediate result through unchanged.  Applying
identity
to arrays:julia> arr = [1, 2, 3, 4]; julia> result = map(identity, arr); julia> result 4element Array{Int64,1}: 1 2 3 4
It can be used with
map
to create a new array with the same elements.
Common mistake example:
julia> identity(1, 2)
ERROR: MethodError: no method matching identity(::Int64, ::Int64)
In this example, the identity
function is called with two arguments, but it only accepts a single argument. Make sure to provide only one argument to the identity
function.
See Also
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