Last week, in general forum someone introduced the possibility to
implement the .? operator in D:
https://forum.dlang.org/thread/blnjoaleswqnaojou...@forum.dlang.org
I decided to implement a simple solution with a funciontal syntax:
string fatherName =
dot(person).dot(a=>a.father).dot(a=>a.name).get("unknown");
Person grandFather =
dot(person).dot(a=>a.father).dot(a=>a.father).get;
That are equivalent to (dart code)
String fatherName = person?.father?.name??"unknown"
Person grandFather = person?.father?.father
The code is
auto dot(T)(T t){ return Dot!T(t); }
struct Dot(T) {
private Nullable!T value; // = Nullable!T.init;
this (T v)
{
static if(isAssignable!(T, typeof(null) ))
{
if(v !is null){
value = nullable(v);
}
} else {
value = nullable(v);
}
}
template dot(R)
{
Dot!R dot( R function(T) fun)
{
static assert(!isAssignable!(typeof(null), R), "Sorry, f
returning type can't be typeof(null)");
return value.isNull() ?
Dot!R() :
Dot!R(fun(value.get()));
}
}
}
T get(T defaultValue)
{
return this.value.get(defaultValue);
}
static if(isAssignable!(T, typeof(null) ))
{
T get()
{
return this.value.isNull ? null : this.value.get;
}
}
}
I tried to adapt to template syntax (as a syntax sugar):
auto name = dot(person).dt!"a.father".dt!"a.father".get;
but I have not succeeded
Example: I tried with a global function
Dot!R dt(alias fun, T, R)(Dot!T t){
auto f = cast(R function(T)) unaryFun!fun;
return t.dot!R(f);
}
I really need to investigate more about unaryFun! :-)
I will appreciate any idea/guidance
Thank you!!!
