format_number.jl

# This was my version of Formatting.jl's `format(..., comma = true)`
# I did this for fun, not having a look at Formatting.jl's version
# It looks like this is how they did it:
# https://github.com/JuliaIO/Formatting.jl/blob/master/src/cformat.jl#L77-L93
# Quite different to how I did it...probably benchmarks better though

function format_number(n::String, delim::Union{Char, S}) where {S <: AbstractString}
    len = length(n)
    io = IOBuffer()
    for (i, c) in enumerate(reverse(n))
        print(io, c)
        if iszero(mod(i, 3)) && i != len
            print(io, delim)
        end
    end
    return reverse(String(take!(io)))
end

function format_number2(n::String, delim::Union{Char, S}) where {S <: AbstractString}
    len = length(n)
    io = IOBuffer()
    for (i, c) in enumerate(reverse(n))
        print(io, c)
        if iszero(mod(i, 3)) && i != len
            print(io, delim)
        end
    end
    return String(reverse(take!(io)))
end

function format_number3(n::String, delim::Union{Char, S}) where {S <: AbstractString}
    len = length(n)
    io = IOBuffer()
    for (i, c) in enumerate(n)
        print(io, c)
        if iszero(mod(len - i, 3)) && i != len
            print(io, ',')
        end
    end
    return String(take!(io))
end

for i in 1:3
    fname = Symbol("format_number$i")
    @eval $fname(n::T, delim::Union{Char, S}) where {T <: Integer, S <: AbstractString} = $fname(string(n), delim)
    @eval $fname(n::T) where {T <: Integer} = $fname(n, ',')
end