Hi!
I've changed Adam D Ruppes module notnull.d a bit to allow
assignment of a NotNull inherited class instance to a NotNull
base class using
/** Assignment from $(D NotNull) Inherited Class $(D rhs) to
$(D NotNull) Base
Class $(D this). */
typeof(this) opAssign(U)(NotNull!U rhs) @safe pure nothrow if
(isAssignable!(T, U)) {
this._value = rhs._value;
return this;
}
This allows
unittest
{
class A {}
class B : A {}
NotNull!B b = assumeNotNull(new B);
NotNull!A a = assumeNotNull(new A);
a = b;
assert(a is b);
}
However I haven't figure out how to allow the follow code to
compile
unittest
{
class A {}
class B : A {}
void f(NotNull!A a) {}
NotNull!B b = assumeNotNull(new B);
f(b);
}
which I believe should work automatically.
How do I make that happen?
Complete source of module notnull.d follows:
#!/usr/bin/env rdmd
module notnull;
import std.traits: isAssignable;
/** Note that NotNull!T is not NotNullable :) */
alias NotNullable(T) = isAssignable!(T, typeof(null));
/**
NotNull ensures a null value can never be stored.
* You must initialize it when declared
* You must never assign the null literal to it (this is a
compile time error)
* If you assign a null value at runtime to it, it will
immediately throw an Error
at the point of assignment.
NotNull!T can be substituted for T at any time, but T cannot
become
NotNull without some attention: either declaring NotNull!T, or
using
the convenience function, notNull.
Condition: T must be a reference type.
Instead of: __traits(compiles, { T t; assert(t is null); }.
TODO: Merge with http://arsdnet.net/dcode/notnullsimplified.d
Examples:
---
int myInt;
NotNull!(int *) not_null = myInt;
// you can now use variable not_null anywhere you would
// have used a regular int*, but with the assurance that
// it never stored null.
---
*/
struct NotNull(T) if (NotNullable!T)
{
@disable this(); // Disallow default initialized (to null)
/** Assignment from $(D NotNull) Inherited Class $(D rhs) to
$(D NotNull) Base
Class $(D this). */
typeof(this) opAssign(U)(NotNull!U rhs) @safe pure nothrow if
(isAssignable!(T, U)) {
this._value = rhs._value;
return this;
}
NotNull!U opCast(U)() @safe pure nothrow if (isAssignable!(U,
T)) {
return NotNull!_value;
}
// this could arguably break the static type check because
// you can assign it from a variable that is null.. but I
// think it is important that NotNull!Object = new Object();
// works, without having to say assumeNotNull(new Object())
// for convenience of using with local variables.
/// Constructs with a runtime not null check (via assert()).
this(T value) @safe pure nothrow
{
assert(value !is null);
_value = value;
}
/** Disable null construction. */
@disable this(typeof(null));
/** Disable null assignment. */
@disable typeof(this) opAssign(typeof(null));
private T _value;
@property inout(T) _valueHelper() inout
{
assert(_value !is null); // sanity check of invariant
return _value;
}
// Apparently a compiler bug - the invariant being
uncommented breaks all kinds of stuff.
// invariant() { assert(_value !is null); }
alias _valueHelper this; /// this is substitutable for the
regular (nullable) type
/* void toMsgpack (Packer) (ref Packer packer) const {
packer.pack(_value); } */
/* void fromMsgpack(Unpacker)(auto ref Unpacker unpacker) {
unpacker.unpack(_value); } */
}
/** A convenience function to construct a NotNull value from
something $(D t)
you know isn't null.
*/
NotNull!T assumeNotNull(T)(T t) if (NotNullable!T)
{
return NotNull!T(t); // note the constructor asserts it is
not null
}
/** A convenience function to check for null $(D t). If you pass
null to $(D t),
it will throw an exception. Otherwise, return NotNull!T.
*/
NotNull!T enforceNotNull(T, string file = __FILE__, size_t line =
__LINE__)(T t) if (NotNullable!T)
{
import std.exception: enforce;
enforce(t !is null, t is null!, file, line);
return NotNull!T(t);
}
unittest
{
import core.exception;
import std.exception;
void NotNullCompiliationTest1()() // I'm making these
templates to defer compiling them
{
NotNull!(int*) defaultInitiliation; // should fail
because this would be null otherwise
}
assert(!__traits(compiles, NotNullCompiliationTest1!()()));
void NotNullCompiliationTest2()()
{
NotNull!(int*) defaultInitiliation = null; // should fail
here too at compile time
}
assert(!__traits(compiles, NotNullCompiliationTest2!()()));
int dummy;
NotNull!(int*) foo = dummy;
assert(!__traits(compiles, foo = null)); // again, literal
null is caught at compile time
int* test;
test = dummy;
