Delphi TDictionary with generics - dictionary

Question

I need a container with different TProc indexed by String.
Something like TDictionary.
TMessageBus = class
private
fContainer: TDictionary<String, TProc<T>>; // ERROR !!
public
procedure Send<T>(aName: String; aData: T); // producer
procedure Subscribe<T>(aName: String; aProc: TProc<T>); // consumer
end;
Please help.

Answer 1

If you have a field dependent on the generic type T you have to make the complete class generic and not the methods:
type
TMessageBus<T> = class
private
fContainer: TDictionary<String, TProc<T>>; // ERROR !!
public
procedure Send(aName: String; aData: T); // producer
procedure Subscribe(aName: String; aProc: TProc<T>); // consumer
end;

Answer 2

Knowing that TProc<T> is implemented as interface you can write this code:
type
TMessageBus = class
private
fContainer: TDictionary<string, IInterface>;
public
constructor Create;
destructor Destroy; override;
procedure Send<T>(const aName: string; const aData: T);
procedure Subscribe<T>(const aName: string; const aProc: TProc<T>);
end;
constructor TMessageBus.Create;
begin
fContainer := TDictionary<string, IInterface>.Create;
end;
destructor TMessageBus.Destroy;
begin
fContainer.Free;
inherited;
end;
procedure TMessageBus.Send<T>(const aName: string; const aData: T);
begin
TProc<T>(fContainer[aName])(aData);
end;
procedure TMessageBus.Subscribe<T>(const aName: string; const aProc: TProc<T>);
begin
fContainer.AddOrSetValue(aName, IInterface(PPointer(#aProc)^));
end;
However apart from leaving out any validation code this can easily blow up if you do send a different data type than you subscribed. So I would use the TValue type here to wrap the passed TProc<T> inside a TProc<TValue> (from System.Rtti). Keep in mind however that TValue itself only allows type conversions that also the compiler allows, so it won't convert string to Integer and alike - but if required you can then add this yourself:
type
TMessageBus = class
private
fContainer: TDictionary<string, TProc<TValue>>;
public
constructor Create;
destructor Destroy; override;
procedure Send<T>(const aName: string; const aData: T);
procedure Subscribe<T>(const aName: string; const aProc: TProc<T>);
end;
constructor TMessageBus.Create;
begin
fContainer := TDictionary<string, TProc<TValue>>.Create;
end;
destructor TMessageBus.Destroy;
begin
fContainer.Free;
inherited;
end;
procedure TMessageBus.Send<T>(const aName: string; const aData: T);
var
proc: TProc<TValue>;
begin
if fContainer.TryGetValue(aName, proc) then
proc(TValue.From<T>(aData));
end;
procedure TMessageBus.Subscribe<T>(const aName: string; const aProc: TProc<T>);
begin
fContainer.AddOrSetValue(aName,
procedure(aValue: TValue)
begin
aProc(aValue.AsType<T>);
end);
end;
If you now call mb.Send('somestring', 42); for example it will raise an EInvalidCast exception in TValue.AsType because as mentioned before it can't convert the passed 42 to string which is what you specified when you called Subscribe.