Hello, how to calculate a constant the first time a function is called? not when compiling not every call foo() = (sleep(1); 1) # foo calculate a constant bar(x) = foo() + x # ???? # first call: @time bar(2) # -> 1.001082 seconds (5 allocations: 144 bytes) # second call: @time bar(2) # -> 0.…

If your function has some input, you might better avoid at all this global state, and wrap the constant precomputed in the input, such that the function is completely self-contained. Something like: julia> struct MyInput x::Vector{Float64} constant::Float64 end julia> …

may be, i dont know but looks like *hit global FOO = nothing # foo() = (sleep(1); global FOO = 1) # foo calculate a constant bar(x) = try FOO + x catch foo() @eval bar(x) = $FOO + x return FOO + x end @time bar(22) # -> 1.001544 seconds (247 allocations: 12.344 KiB) @time bar…

Here’s a pretty simple way to do it: const FOO = Ref{Union{Int, Nothing}}(nothing) function foo() if FOO[] === nothing println("expensive calculation running...") sleep(1) FOO[] = 1 end FOO[] end bar(x) = foo() + x Demo: julia> bar(1) expensive calculation running... 2 julia> …

Or, if you do not trust union splitting, you can have one global with a boolean to indicate if the function was already called or not; and the global with the Ref starting with a dummy/undef value.

How to calculate a constant the first time a function is called?

General Usage

lmiq March 7, 2022, 1:55pm 3

see this thread: In Julia, how to create a function that saves its own internal state?

1 Like

Topic		Replies	Views
Define a Julia function New to Julia question , functions	10	848	February 9, 2022
"`const static`" function parameters General Usage	31	4544	November 9, 2017
How to make a function store data to avoid repeating computation General Usage question , functions , style , memoize	45	2085	October 17, 2022
On modules and globals General Usage module	14	907	January 8, 2022
Efficient definition of function which uses fixed allocated constants General Usage	2	106	April 11, 2025

How to calculate a constant the first time a function is called?

Related topics