Use Returns instead of this package

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ConstantFunctions

Usage

ConstantFunction(v) models a constant function always returning the value v.

The functions value can be accessed by providing either zero or one (arbitrary) argument:

f = ConstantFunction(10)

f(3) # 10
f() # 10

It can also be multiplied:

f = ConstantFunction(10)
g = 3*f

g isa ConstantFunction # true
g() # 30

Motivation

This is useful if you use a type with functions, with a special treatment for constant functions. Here is an example.

struct DifferentialEquation{TF<:Function}
    λ::TF
end

function solve(eq::DifferentialEquation, x0)
    # solve x' = λ(x) x
    # with initial condition x(0) = x0
end

# special case of constant functions
solve(eq::DifferentialEquation{<:ConstantFunction}, x0) = exp(eq.λ())*x0