Support mapping from Dictionary<string, object?>

[latonz]

Add support for mappings with a class/struct target and a source implementing IReadOnlyDictionary<string, TValue> or IDictionary<string, TValue> with TValue beeing either object or object?.

Questions to be discussed:

• What type conversions should be supported? => For now only casting.
• What happens with required but unmapped members? => throw an exception
• What happens if a value is provided for a member but it cannot be converted to the target type? => throw an exception
• How to map nested objects?

Example

Definition

public class Fruit
{
    public required string Name { get; init; }
    public int Weight { get; set; }
    public Color Color { get; set; }
}

public enum Color { Red, Green }

[Mapper]
public partial class MyMapper
{
    public partial Apple Map(IReadOnlyDictionary<string, object?> source);
}

Generated code

public partial class MyMapper
{
    public partial Apple Map(IReadOnlyDictionary<string, object?> source)
    {
        var target = new Apple
        {
            Name = (string)source.GetValueOrDefault(nameof(Apple.Name)) ?? throw ...
        };
        if (source.TryGetValue(nameof(Apple.Weight), out var weight))
        {
            target.Weight = (int)weight;
        }
        if (source.TryGetValue(nameof(Apple.Color), out var color))
        {
            target.Color = (Color)color;
        }
        return weight;
    }

    private partial int ParseString(string source)
    {
        return int.Parse(source);
    }

    private partial Color ParseColor(string source)
    {
         return source switch
         {
             nameof(Color.Red) => Color.Red,
             nameof(Color.Green) => Color.Green,
             _ => throw ...
         };
    }
}

Rel. #1041 and #1039

[leoerlandsson]

Interesting, I was just looking for this functionality :D

The other way around would be useful aswell, i.e mapping from an object to a Dictionary.