Hi golang-nuts,
I am trying out the latest type parameter, and type sets design.
The purpose is to implement a Clamp function that works for numbers and vectors.
The version for numbers is straightforward and easy:
```go
// Number is a type set of numbers.
type Number interface {
~int | ~int8 | ~int32 | ~int64 | ~float32 | ~float64
}
// Clamp clamps a given value in [min, max].
func Clamp[N Number](n, min, max N) N {
if n < min { return min }
if n > max { return max }
return n
}
```
Everything is good so far. Then, let's define vector types:
```go
// Vec2 represents a 2D vector (x, y).
type Vec2[N Number] struct {
X, Y N
}
// Vec3 represents a 3D vector (x, y, z).
type Vec3[N Number] struct {
X, Y, Z N
}
// Vec4 represents homogeneous coordinates (x, y, z, w) that defines
// either a point (W=1) or a vector (W=0). Other cases of W need to apply
// a perspective division to get the actual coordinates of X, Y, Z.
type Vec4[N Number] struct {
X, Y, Z, W N
}
```
However, to declare a type set of all possible vectors, I tried
two possibilities:
```go
// Vec is a type set of vectors.
type Vec[N Number] interface {
Vec2[N] | Vec3[N] | Vec4[N] // ERROR: interface cannot have type parameters
}
```
```go
type Vec interface {
Vec2[N Number] | Vec3[N Number] | Vec4[N Number] // ERROR: interface cannot
have type parameters
}
```
Let's enumerates all possibilities for the Vec type set:
```go
// Vec is a type set of vectors.
type Vec interface {
Vec2[float32] | Vec3[float32] | Vec4[float32] |
Vec2[float64] | Vec3[float64] | Vec4[float64]
}
```
However, with this definition, it remains very tricky to construct a
generic implementation for a clamp function:
```go
// ERROR: this function does not compile
func ClampVec[V Vec, N Number](v V, min, max N) V {
switch (interface{})(v).(type) {
case Vec2[float32]:
return Vec2[float32]{
Clamp[float32](v.X, min, max),
Clamp[float32](v.Y, min, max),
}
case Vec2[float64]:
return Vec2[float64]{
Clamp[float64](v.X, min, max),
Clamp[float64](v.Y, min, max),
}
case Vec3[float32]:
return Vec3[float32]{
Clamp[float32](v.X, min, max),
Clamp[float32](v.Y, min, max),
Clamp[float32](v.Z, min, max),
}
case Vec3[float64]:
return Vec3[float64]{
Clamp[float64](v.X, min, max),
Clamp[float64](v.Y, min, max),
Clamp[float64](v.Z, min, max),
}
case Vec4[float32]:
return Vec4[float32]{
Clamp[float32](v.X, min, max),
Clamp[float32](v.Y, min, max),
Clamp[float32](v.Z, min, max),
Clamp[float32](v.W, min, max),
}
case Vec4[float64]:
return Clamp[float64]{
Clamp[float64](v.X, min, max),
Clamp[float64](v.Y, min, max),
Clamp[float64](v.Z, min, max),
Clamp[float64](v.W, min, max),
}
default:
panic(fmt.Sprintf("unexpected type %T", v))
}
}
```
I wish I could converge to a version similar like this:
```go
func Clamp[N Number](n, min, max N) N {
if n < min { return min }
if n > max { return max }
return n
}
// ERROR: this functions does not compile
func ClampVec[N Number, V Vec[N]](v V[N], min, max N) V[N] {
switch (interface{})(v).(type) {
case Vec2[N]: // If V is Vec2[N], then return a Vec2[N].
return Vec2[N]{
Clamp[N](v.X, min, max),
Clamp[N](v.Y, min, max),
}
case Vec3[N]: // Similar
return Vec3[N]{
Clamp[N](v.X, min, max),
Clamp[N](v.Y, min, max),
Clamp[N](v.Z, min, max),
}
case Vec4[N]: // Similar
return Vec4[N]{
Clamp[N](v.X, min, max),
Clamp[N](v.Y, min, max),
Clamp[N](v.Z, min, max),
Clamp[N](v.W, min, max),
}
default:
panic(fmt.Sprintf("unexpected type %T", v))
}
}
// caller side:
Clamp[float32](256, 0, 255) // 255
Clamp[float64, Vec2[float64]]({1, 2, 3}, 0, 1) // Vec2[float32]{1, 1, 1}
...
```
I found myself trapped and not able to proceed further.
- Is the above code legal with the current design but
because the compiler has not implemented it yet?
- Any ideas on how could the current design be able to produce something even
simpler?
- If it is impossible to archive a similar implementation, what could be the
best practices to implement a generic clamp function?
Thank you in advance for your read and help.
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