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 | Posted by ArturG |  Permalink Reply |
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ArturG 
| ive read some discussions about some library solution for the ?. operator,
has there been anything added to phobos?
wouldnt a checked with expression be a more general/longer form of the ?. operator?
A with expression not only allows you to do unchecked/checked access to members but to any operation you can do on the type,
it allows method/statement cascading so that you dont have to return this from methods,
thereby you can combine it with function chaining without breaking the cascading,
and it can also be used to wrap any statement to integrate them into a function chain.
some example syntax:
T t = T # { /*same as with statement*/ }; // works only with aggregate types, returns its input
T t = T #aliasName { }; // works with any type, can use aliasName to refer to the input like self/this, returns its input
RetType t = T #aliasName, RetType varName { }; // same as above but can change the return type
// extention for the above, checks the input before executing the block,
// if input is null/false the block does'nt get executed the return value will be null/T.init/RetType.init
T t = T #? { };
T t = T #?aliasName { };
RetType t = T #?aliasName, RetType varName { };
// optionally
#{ /*empty with expression*/ }; // originally not planned but would work like the statement expression
// mentioned in the kill the comma operator thread, no input no output and allways runs block
// for single operations, the short null checked version is less verbose
t?.foo = 5; // if t is null no assignment happens,
// same as if(t) t.foo = 5; or t#?{ foo = 5; };
t.child = s?.child; // if s is null, t.child will be null,
// same as t.child = s? s.child : null; or t.child = s#?_, typeof(t.child) ret{ ret = child;};
t?.child = s?.child?; // if t is null no assignment, if s or s.child is null, t.child will be null,
// same as if(t) t.child = (s && s.child)? s.child : null; or t#?lhs{ s#? { child#?rhs{ lhs.child = rhs; };};};
-----------------------------------------
some examples:
// using it with aggregate types
struct Foo{ string name; int val; }
class Bar{ string name; int val; }
Foo()#{ name = "Foo"; val = 5; }.writeln;
new Foo() #
{
import std.string : capitalize;
name = someName.capitalize;
val = 5;
}.writeln;
auto foo = Foo()#n{ name = "Foo"; val = 5; n.writeln; };
new Bar#{ name = "Foo"; val = 5; }.writeln;
auto bar = new Bar#{ name = "Foo"; val = 5; };
auto someBar = (someCond? getBar() : new Bar) #{ name = "Bar"; val = 30; };
auto someBar = getBar.or(new Bar) #{ name = "Bar"; val = 30; };
auto dg = (string s, int v) => new Bar#{ name = s; val = v; };
// some other random uses
"test"#n{ import std.string; n.capitalize; }.writeln;
66#n, string ret{ import std.conv; ret = n.to!string; }.foo();
// writes the return value of someFun
someFun()#n{ n == 5? doSomething() :
n == 6? doSomethingElse() : null; }.writeln;
// writes five or six or no match
someFun()#n, string ret{ ret = n == 5? "five" :
n == 6? "six" : "no match"; }.writeln;
auto res = someFun.someOtherFun #n{ foreach(i; 0 .. n) i.writeln; }.fun(6) #n{ n.writeln; };
//void fun(string name, int val, string, int);
wrap!fun#{ name = "Test"; param2 = "some string";
param3 = 66; val = 2; }();
auto wrappedFun = wrap!fun#{
name = "test";
param2 = "some string";
param3 = 66;
val = 2;
};
wrappedFun.param0 = "Test";
wrappedFun.param2 = "some other string";
wrappedFun.val = 70;
wrappedFun();
// if(c.foo) c.foo.x = 55;
c.foo?.x = 55;
c.foo#?{ x = 55; };
// if(someClass && someClass.child && someClass.child.child &&
// someOtherClass && someOtherClass.child && someOtherClass.child.child)
// { someClass.child.child.x = someOtherClass.child.child.x * 2; }
someClass?.child?.child?.x = someOtherClass?.child?.child?.x * 2;
someClass#?{ child#?{ child#?lhs {
someOtherClass#?{ child#?{ child#?rhs {
lhs.x = rhs.x * 2;
};};};};};};
//if(someClass) with(someClass){
// x = 5; x.writeln;
// if(child) with(child){
// x = 6; x.writeln;
// alias lhs = child;
// if(child) with(child){
// if(someOtherClass) with(someOtherClass){
// x = 10; x.writeln;
// if(child) with(child){
// x = 59; x.writeln;
// if(child) with(child){
// lhs.x = x * 2;
// x = 44; x.writeln;
//} } } } } }
// same as above
someClass #? { x = 5; x.writeln;
child #? { x = 6; x.writeln;
child #?lhs {
someOtherClass #? { x = 10; x.writeln;
child #? { x = 59; x.writeln;
child #? { lhs.x = x * 2; x = 44; x.writeln;
}; }; }; }; }; };
// empty with expression, when you dont need a input and output basically just a scope as a expression
for(size_t i; i < 10; #{ i++; i.writeln; })
{}
here some templates which implement parts of the above behavior
import std.functional : unaryFun;
auto then(alias fun, T)(T type) if(is(typeof(unaryFun!fun)))
{
import std.traits : ReturnType;
static if(is(ReturnType!(fun!T) == void))
{
fun(type);
return type;
}
else
{
return fun(type);
}
}
auto checkThen(alias fun, T)(T type) if(is(typeof(unaryFun!fun)))
{
import std.traits : ReturnType, isFloatingPoint;
static if(is(ReturnType!(fun!T) == void))
{
static if(isFloatingPoint!T)
{ import std.math : isNaN;
if(type.isNaN) return type;
}
if(type) fun(type);
return type;
}
else
{
static if(isFloatingPoint!T)
{ import std.math : isNaN;
if(type.isNaN) return ReturnType!(fun!T).init;
}
return type? fun(type) : ReturnType!(fun!T).init;
}
}
example comparing the above templates and with expression:
original example from dlangui using mostly dml: https://github.com/buggins/dlangui/blob/master/examples/helloworld/src/helloworld.d
with expression: https://dpaste.dzfl.pl/15f767d91212
templates: https://dpaste.dzfl.pl/5648204131c8
would something like this be usefull?
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