add utilities for applying options and copying protobufs

[paulwe]

No description provided.

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[boks1971]

Sorry Paul, I already asked you this once, but I forgot the answer :-(. What does the ~ mean there?

[paulwe]

~ means the type constraint permits any type with the same underlying type. so for example

type Foo func()

var f0 = func() {}
var f1 Foo = func() {}

func a[T ~func()](f T) {}
func b[T func()](f T)  {}

a(f0) // ok
b(f0) // ok
a(f1) // ok
b(f1) // not ok

[boks1971]

ah, got it. Thank you Paul. Let me commit this to my poor memory and hope it survives till the next time I see this pattern :-)

[paulwe]

this is needed here because we have functional options like

type FooOption func(x *FooOptions)

// several implementations of FooOption

func SomeFoo(opts ...FooOption) {
    _ := options.Apply(&FooOptions{}, opts)
    // without ~ this wouldn't work because []FooOption is not []func(*FooOptions)
}

[boks1971]

nice!!!