method vs lambda

definitions.jl

f(x::Int) = "$x is an integer"
f(x::String) = "$x is a string"

g = x::Int -> "$x is an integer"
g = x::String -> "$x is a string"

repl.jl

julia> f(123)
"123 is an integer"

julia> f("hi")
"hi is a string"

julia> f = "oops, constant"
ERROR: invalid redefinition of constant f
Stacktrace:
 [1] top-level scope at REPL[7]:1

julia> g(123)
ERROR: MethodError: no method matching (::getfield(Main, Symbol("##5#6")))(::Int64)
Closest candidates are:
  #5(::String) at REPL[4]:1
Stacktrace:
 [1] top-level scope at REPL[8]:1

julia> g("hi")
"hi is a string"

julia> g = "this is fine"
"this is fine"

Explanation:

• f has multiple methods—it can be called on both Ints or Strings
• f is a constant binding and cannot be reassigned
• g is non-constant and takes on three different values:
  1. an anonymous function that can be called only on Ints
  2. an anonymous function that can be called only on Strings
  3. the string "this is fine"