add FT wrapper for scalars

[haakon-e]

Purpose

Add macro @convert_scalars to conveniently wrap scalars (e.g. integers, floats) with the provided FT, e.g.:

FT = Float32
@convert_scalars FT 1 + 2.0 + 3.0f0 * π + sin(pi)
# expands to: FT(1) + FT(2.0) + FT(3.0f0) * FT(π) + sin(FT(pi))

[charleskawczynski]

Where is this intended to be used?

[haakon-e]

I wanted this for some functions I'll be writing that provide forcing / boundary conditions for the LES. They will look similar to (but mine have more terms needing to be wrapped in FT) e.g.

ClimaAtmos.jl/src/initial_conditions/initial_conditions.jl

Lines 646 to 650 in 0ee96c0

	draft_area(::Type{FT}) where {FT} =
	z -> z < 0.7e4 ? FT(0.5) * exp(-(z - FT(4e3))^2 / 2 / FT(1e3)^2) : FT(0)
	edmfx_q_tot(::Type{FT}) where {FT} =
	z -> z < 0.7e4 ? FT(1e-3) * exp(-(z - FT(4e3))^2 / 2 / FT(1e3)^2) : FT(0)

which (in the case of the example above), would become something like

edmfx_q_tot(::Type{FT}) where {FT} = @convert_scalars FT z ->
    z < 0.7e4 ? 1e-3 * exp(-(z - 4e3)^2 / 2 / 1e3^2) : 0

edmfx_q_tot(::Type{FT}) where {FT} = @convert_scalars FT z ->
    z < 0.7e4 ? 1e-3 * exp(-(z - 4e3)^2 / 2 / 1e3^2) : 0

An example of what I will actually do is:

FT = eltype(params)
θ = @convert_scalars FT z -> if z < 400 # m
    265 + 0.004 * (z - 400)
elseif 400 ≤ z < 825
    265
elseif 825 ≤ z < 2045
    266 + (z - 825)^0.3
elseif 2045 ≤ z
    271 + (z - 2000)^0.33
end

[dennisYatunin]

I'd recommend using something like names(MathConstants)[2:end] instead of manually listing out :π, :pi, etc.