/// <summary>
/// Subtract the Some(x) of one option from the Some(y) of another.
/// For numeric values the behaviour is to find the difference between the Somes (lhs - rhs)
/// For Lst values the behaviour is to remove items in the rhs from the lhs
/// For Map or Set values the behaviour is to remove items in the rhs from the lhs
/// Otherwise if the T type derives from ISubtractable then the behaviour
/// is to call lhs.Subtract(rhs);
/// </summary>
/// <param name="lhs">Left-hand side of the operation</param>
/// <param name="rhs">Right-hand side of the operation</param>
/// <returns>lhs - rhs</returns>
public static T?subtract <T>(T?lhs, T?rhs) where T : struct
{
if (!lhs.HasValue)
{
return(rhs);
}
if (!rhs.HasValue)
{
return(lhs);
}
return(TypeDesc.Subtract(lhs.Value, rhs.Value, TypeDesc <T> .Default));
}
/// <summary>
/// Subtract the Some(x) of one option from the Some(y) of another.
/// For numeric values the behaviour is to find the difference between the Somes (lhs - rhs)
/// For Lst values the behaviour is to remove items in the rhs from the lhs
/// For Map or Set values the behaviour is to remove items in the rhs from the lhs
/// Otherwise if the T type derives from ISubtractable then the behaviour
/// is to call lhs.Subtract(rhs);
/// </summary>
/// <param name="lhs">Left-hand side of the operation</param>
/// <param name="rhs">Right-hand side of the operation</param>
/// <returns>lhs - rhs</returns>
public OptionUnsafe <T> Subtract(OptionUnsafe <T> rhs)
{
var self = IsNone
? TypeDesc <T> .Default.HasZero
? Some(TypeDesc <T> .Default.Zero <T>())
: this
: this;
if (self.IsNone)
{
return(this); // zero - rhs = undefined (when HasZero == false)
}
if (rhs.IsNone)
{
return(this); // lhs + zero = lhs
}
return(TypeDesc.Subtract(self.Value, rhs.Value, TypeDesc <T> .Default));
}
public NewType <T> Subtract(NewType <T> rhs) =>
GetType() == rhs.GetType()
? (NewType <T>) NewType.Construct(GetType(), TypeDesc.Subtract(Value, rhs.Value, TypeDesc <T> .Default))
: failwith <NewType <T> >("Mismatched NewTypes in subtract");