C# FieldInfo reflection alternatives

问题:

I am currently using FieldInfo.GetValue and FieldInfo.SetValue quite a lot in my programm, which is significantly slowing up my programm.

For PropertyInfo I use the GetValueGetter and GetValueSetter methods so I only use reflection once for a given type. For the FieldInfo, the methods don't exist.

What is the suggested approach for FieldInfo?

EDIT: I followed this useful link from CodeCaster's reply. This is a great search direction.

Now the "only" point that I don't get in this answer is how I can cache the getters / setters and re-use them in a generic way, using only the field's name - which is basically what the SetValue is doing

// generate the cache
Dictionary<string, object> setters = new Dictionary<string, object>();
Type t = this.GetType();
foreach (FieldInfo fld in t.GetFields()) {
     MethodInfo method = t.GetMethod("CreateSetter");
     MethodInfo genericMethod = method.MakeGenericMethod( new Type[] {this.GetType(), fld.FieldType});
     setters.Add(fld.Name, genericMethod.Invoke(null, new[] {fld}));
}
// now how would I use these setters?
setters[fld.Name].Invoke(this, new object[] {newValue}); // => doesn't work without cast....

回答1:

You could use Expressions to generate faster field accessors. If you want them to work on Object rather than the field's concrete type, you'd have to add casts (Convert) in the expression.

using System.Linq.Expressions;

class FieldAccessor
{
    private static readonly ParameterExpression fieldParameter = Expression.Parameter(typeof(object));
    private static readonly ParameterExpression ownerParameter = Expression.Parameter(typeof(object));

    public FieldAccessor(Type type, string fieldName)
    {
        var field = type.GetField(fieldName,
            BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
        if (field == null) throw new ArgumentException();

        var fieldExpression = Expression.Field(
            Expression.Convert(ownerParameter, type), field);

        Get = Expression.Lambda<Func<object, object>>(
            Expression.Convert(fieldExpression, typeof(object)),
            ownerParameter).Compile();

        Set = Expression.Lambda<Action<object, object>>(
            Expression.Assign(fieldExpression,
                Expression.Convert(fieldParameter, field.FieldType)), 
            ownerParameter, fieldParameter).Compile();
    }

    public Func<object, object> Get { get; }

    public Action<object, object> Set { get; }
}

Usage:

class M
{
    private string s;
}

var accessors = new Dictionary<string, FieldAccessor>();

// expensive - you should do this only once
accessors.Add("s", new FieldAccessor(typeof(M), "s"));

var m = new M();
accessors["s"].Set(m, "Foo");
var value = accessors["s"].Get(m);