Design advice

General Usage
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1

Hi,

I would like to hear some design advice. I want the user to pass two parameters to a function where the second parameter depends on the first one. However, for pratical reason, I dont want the user to write a complicated call. Hence, the actual call is like:


struct Algo{T}
    a::T
end

# the way that works
function solve(a = 1.0; options = Algo(a))
    # the solve function 
    @show options.a
end

whereas I would like it to be

solve(a = 1.0; options = Algo())

but Algo() is not defined. Has anyone encountered such question? What have you done?
Thank you for your suggestions,

Best regards,

2

I don’t understand the question: you want options to depend on a, but implement it in a way that doesn’t?

I would go with something like

default_options(a) = A(a) # can customize it later

function solve(a = 1.0; options = default_options(a))
    @show options
end

then document and expose default_options as part of the API, so if the user wants to customize things the whole thing is clean and transparent.

3

I wrote A(a) instead of A().

4

I know it sounds reasonable (altough less if you think that a is a struct with 10 fields and Algo depends on one of those fields), this is what I proposed. But is seems clunky (he has to pass a twice) to me as the user has to know the internals of A.

5

Something like

const default_option = ...

function solve(a = 1.0; options = default_option)
     options = Algo(a, options)
end

or something then?

You can do whatever you want in Algo then and the user only passes in the one field.

6

Not sure. My MWE seems too minimal. There are many algorithm (aka struct) the user can pass. There is Algo1, Algo2…

My problem originates from my package where I want the user to pass a linearsolver (ie a in the above MWE) and also a Bordered linear solver (ie Algo1, Algo2… above) which depends on the linear solver passed by the user. But somehow, I was wondering how to make the user pass the linearalgo only once to solve.

Right now, in package, the linear bordered solver is pass with a Symbol. I would like to remove this and all the if in here.

7

This seems to be the crux and is the cause of the repeating. You have a both by itself and also shoved in another object. That seems unnecessary. Couldn’t it be something like

function solve(solver = LinearSolver();  options = Algorithm())
     create_final_object(solver, options)
end

That is, the Algorithm() object doesn’t need to know about solver. But inside the body of the function you are free to mix these however you want.

1 Like
8

Yes I like it! Thank you.