Swift : Conditional assignment operators

ConditionalAssignmentOperators.swift

// MARK: - Not nulling assignment

precedencegroup NotNullingAssignment
{
    associativity: right
}

// This operators does only perform assignment if the value (right side) is not null.
infix operator =?: NotNullingAssignment

public func =?<T>(variable: inout T, value: T?)
{
    if let value = value
    {
        variable = value
    }
}

// This case is also necessary, because the previous one does not work is `variable`
/// is also optional, because in this case `T` would represent an optional.
public func =?<T>(variable: inout T?, value: T?)
{
    if let value = value
    {
        variable = value
    }
}

// MARK: - Not crushing assignment

precedencegroup NotCrushingAssignment
{
    associativity: right
}

// This operators does only perform assignment if the variable (left side) is null.
infix operator ?=: NotCrushingAssignment

public func ?=<T>(variable: inout T?, value: T)
{
    if variable == nil
    {
        variable = value
    }
}

/// This case is also necessary, because the previous one does not work is `variable`
/// is also optional, because in this case `T` would represent an optional.
public func ?=<T>(variable: inout T?, value: T?)
{
    if variable == nil
    {
        variable = value
    }
}

?= : Assignment is performed only if the variable (left side) is null - it does not crush any value.
=? : Assignment is performed only if the new value (right side) is not null.