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[Improvement] - Add by default using optimum constructor selector to unify the choice of constructor for types #892
Description
Since the restriction of having a default constructor new() for classes is no longer mandatory,
and the constructor can using default values for the parameter type.
Optimality criterion(MappingScore) = maximum count of not mapped params. (MappingParam - CountParam)
If any constructors have the same MappingScore, select the one with more parameters.
Edge case: If any constructors have the same equal MappingScore and equal count of params select first.
Example:
Source
{
A
}
Destination
{
new () // MappingScore = 0; ParamCount = 0;
new (A) // MappingScore = 0; ParamCount = 1; <- select this max Param
}
Destination
{
new () // MappingScore = 0; ParamCount = 0; <- select this max MappingScore
new (A,В) // MappingScore = -1; ParamCount = 1;
}
Destination
{
new (A) // MappingScore = 0; ParamCount = 0; <- select this max MappingScore
new (A,В) // MappingScore = -1; ParamCount = 2;
}
Edge case:
Destination
{
new (A,B) // MappingScore = -1; ParamCount = 1; <- select this max MappingScore
new (A,C) // MappingScore = -1; ParamCount = 1;
}
Activity
stagep commentedon Mar 26, 2026
If I understand correctly, select the ctor that has the most parameters that match the source properties. In an edge case, with a tie on the number, you are going with the first ctor based on alphanumeric sorting. Seems more logical then the logic of the person who created the ctors on the destination object.
DocSvartz commentedon Mar 26, 2026
@stagep
This algorithm is use in 7.4.0, but it has one problem.
In this case, it won't select anything because nothing matches.
That's why there should be two criteria = MaxMatched && MinUnmatched. (But in this interpretation it is much more difficult to calculate.)
In my opinion, it's safer to activate a constructor with a one parameter than with two. Because we can't actually know whether the constructor is capable of correctly handling the default value. 😂
*The letters are not for alphabetical order, but simply to show that these are parameters with different or matched names
stagep commentedon Mar 26, 2026
So in the edge case example that you had
either ctor could have been used.
The better question is if we have properties A and B in source and we have ctor A, ctor B, ctor A C, ctor B,C, what ctor would you use?
DocSvartz commentedon Mar 26, 2026
ctor A or ctor B, depending on which one was written first in the source code.
Apparently, this is how typeof(Test).GetConstructors() works.
But I'm not sure maybe it sorts is alphabetically.
DocSvartz commentedon Mar 26, 2026
I was, of course, referring to
.GetConstructors().😑You could, of course, add alphabetical sorting, but I don't really see the point.
It doesn't reduce the risk of non-operability, plus there's added extra costs of additional sorting.🤔
stagep commentedon Mar 26, 2026
Being nondeterministic within Mapster is fine. Don't add overhead.