我正在使用Xcode 8和Swift 3。
我正在尝试为QVector3D oldVec = QVector3D(x,y,z); //this is your 3x1 vertex position
QVector4D newVec = QVector4D(oldVec.x(), oldVec.y(), oldVec.z(), 1); //added 1 as fourth component
QVector4D transformedVec = matrix*newVec; //matrix is your 4x4 transformation matrix
//transformedVec is now what you need but with the fourth component still being the 1, so we just leave it out:
QVector3D transformedVec3D = QVector3D(transformedVec.x(), transformedVec.y(), transformedVec.z());
编写扩展功能，但前提是元素类型为Sequence。下面是一个非扩展功能，显示了我想要的功能：
MyGenericClass<Value>我尝试了以下操作：
public class MyGenericClass<Value> {
public func generateValue() -> Value { ... }
}
public func myFunction<Value>(_ array: Array<MyGenericClass<Value>>) -> [Value] {
return array.map { generic in generic.generateValue() }
}
但是它给了我错误：extension Sequence {
public func myFunction<Value>() -> [Value] where Iterator.Element: MyGenericClass<Value> {
return map { generic in generic.generateValue() }
}
}
的地图关闭。我猜是因为编译器实际上不是从函数主体中的where子句约束中推断元素类型？