Here is my code:

import Foundation
import Combine

func todo() -> Never{ fatalError("Not Implemented!") }

protocol WASMDecodable{
    init(from decoder: WASMDecoder) throws
}

protocol WASMLeafDecodable: WASMDecodable{}
extension WASMLeafDecodable{
    init(from decoder: any WASMDecoder) throws { self = try decoder.decode(Self.self) }
}

protocol WASMTopLevelDecoder{
    associatedtype Input
    func decode<T: WASMDecodable>(_ type: T.Type, from input: Self.Input) throws -> T
}

protocol WASMDecoder{
    func decode<T: WASMDecodable>(_ type: T.Type) throws -> T
    func decode(_ type: UInt8.Type) throws -> UInt8
}

extension WASMDecoder{
    
}

class WASMBinaryContainer: WASMDecoder{
    
    func decode(_ type: UInt8.Type) throws -> UInt8 {
        todo()
    }
    
    func decode<T>(_ type: T.Type) throws -> T where T : WASMDecodable {
        try T(from: self)
    }
    
}

class WASMBinaryDecoder: WASMTopLevelDecoder{
    func decode<T>(_ type: T.Type = T.self, from input: Data) throws -> T where T : WASMDecodable {
        try WASMBinaryContainer(bytes: input).decode(type)
    }
}

extension UInt8: WASMLeafDecodable{ }

let a: UInt8 = try WASMBinaryDecoder().decode(from: Data([0x01, 0x02]))

The compiler always chose to call the func decode<T>(_ type: T.Type) throws -> T where T : WASMDecodable instead of non-generic one.

Is there a way to let it choose to call the non-generic one.

I try to modify the non-generic one to this:
func decode<T: WASMDecodable>(_ type: T.Type) throws -> T where T == UInt8

But it will only spit out a warning that says this will be an error in swift 6, and will not affect the compiler’s choice.