I am amazed by the value type in Julia and hence wrote a blog post about it. During the writing, some idea came to my mind, and I’ll express it as follows. I want to define the root function in a weird way root( x::Float64, ::Val{n} ) where n which calculates x^{1/n}. This allows me not only to …

Most of the utility of Val occurs when you can use Val{x}() with x known at compile-time (either because it is a literal constant or because it comes from another compile-time value like a type parameter). Then the compiler choses the correct method to call based on x and there is no runtime cost. …

The better way to define Int_root_ofa_Float64 is: root(x::Float64, n::Int) = x^inv(n) because you do not really want to dispatch differently for each value of n. julia> root(x::Float64, n::Int) = x^inv(n) julia> root(x::Float64, n::String) = root(x, Val(Symbol(n))) julia> root(x::Float64, n::Va…

Thanks for the reply, but I still have some doubt. Let’s forget the underlying meaning of root and just consider it as a function. I’ll explain it in two points. The reason of this convoluted definition You have already defined some methods like root(x::Float64, n::Val{:cat}) root(x::Float64, n::…

Note also that in the past there were different attempts at implementing this, one I can remember is this package [image] GitHub - toivoh/PatternDispatch.jl: Method dispatch based on pattern matching... Method dispatch based on pattern matching for Julia - GitHub - toivoh/PatternDispatc…

[image] Wenjie: So, is it actually a good idea, or I overstretched? Some quick remarks: Val types are nothing special, the same pattern applies to parametric (singleton) types. One of the key features of Julia is achieving performance by optimizing code for parametric concrete types. Us…

Upon reading the information provided by @fabiangans and @waldyrious , I understood the difference between type dispatch and pattern dispatch. However, I didn’t find any concept similar to pattern dispatch in other languages (e.g. C++). Is this thing exclusive to Julia? I tried to search for it on G…

You could look at Icon, Prolog for examples of using syntactic patterns to guide the flow of control in a program. fyi here is one appropriate use of Val types (from Base) # Core.Compiler has complicated logic to inline x^2 and x^3 for # numeric types. In terms of Val we can do it much more simp…

Rust has some very advanced mechanism for pattern matching The match Control Flow Operator - The Rust Programming Language but their match does not really resemble pattern method dispatch, but is rather a normal control flow operator, similar to GitHub - kmsquire/Match.jl: Advanced Pattern Matching …

I see. Square and cube have more efficient implementation, and this is also why, in Python, x**2**2 is much faster than x**4. BTW, several lines ( Line 230 ) above the code you quoted read # x^p for any literal integer p is lowered to Base.literal_pow(^, x, Val(p)) # to enable compile-time optimizat…

Help me refine my blog post introducing the value type

General Usage

waldyrious August 22, 2018, 1:28pm 6

There’s been some related discussion here: The relation between pattern matching and multiple dispatch

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Help me refine my blog post introducing the value type

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