Multiple dispatch in Julia

One function name; the method is chosen by every argument's type.

# One function name, one method per argument signature: dispatch
# picks by the types of every argument, not just the first.
describe(m::Real) = "magnitude $m"
describe(name::String) = "target $name"
describe(name::String, m::Real) = "$name at magnitude $m"

println(describe(4.2))
println(describe("Altair"))
println(describe("Altair", 0.76))

# methods() shows the table dispatch chooses from.
println(length(methods(describe)), " methods defined")

How it works

1. Three describe methods differ only in signatures.
2. Calls route by type: a Real, a String, or the pair.
3. methods(describe) lists the table dispatch chooses from.

Keywords and builtins used here

• Real
• String

The run, in numbers

Lines

12

Characters to type

450

Tokens

82

Three-star pace

70 tpm

At the three-star pace of 70 tokens a minute, this run takes about 70 seconds.

Type this snippet

Step 2 of 3 in Functions, step 8 of 27 in Language basics.

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