Assigned delegate

[deanebarker]

Allows the execution of a C# delegate whenever values are assigned via an assign or capture tag.

[sebastienros]

I'd rather separate both, or there is no way to just extend the assign tag only. If someone wants both then the same event can be added to both.

[deanebarker]

How do want them named?

[sebastienros]

Good. It's important we can change the options globally or per context.

[sebastienros]

Like Captured this should return a ValueTask. But unlike Captured, and that's something that could be changed at some point, we should also provide the TemplateContext as an argument because sometimes you need to take the options into account to do something. I have had to add it in the most recent commit I did, and obsolete the previous methods. So let's not miss it here.

[deanebarker]

So, should the delegate be async? (warning: async programming is a weak spot for me...)

[sebastienros]

What it means is the delegate signature needs to return a ValueTask so instead of Action<FluidValue> it becomes a Func<FluidValue, ValueTask>. Then to add TemplateContext as the input, it becomes Func<FluidValue, TemplateContext, ValueTask>.

I will need to help you though for the invokation since there is an early non-async exit (Awaited method) and I don't expect you to know how to handle that (you can try still).

[deanebarker]

...so, I wasn't planning on do anything with the return value. My goal was just to get variables "out" of the template. Do you want something to return and be assigned inside the context?

[sebastienros]

Let me update your PR, you'll see. To make something "async" you just need to return "ValueTask" or "Task", you don't use it, the compiler/runtime will.

[sebastienros]

PR updated. Also modified the Captured delegate with a breaking change, but makes it more powerful.

[deanebarker]

@sebastienros To be totally clear, this is what I'm after. If you want to return the value to the context, that's fine, but goal for this PR was just to get them out.

  [Fact]
  public async Task Assign2()
  {
      var source = @"
          {%- assign a = 'b' %}
          {%- assign c = 'd' %}
      ";

      var dataAssignmentsFromTemplateExecution = new Dictionary<string, object>();

      _parser.TryParse(source, out var template, out var error);
      var context = new TemplateContext
      {
          Assigned = (identifier, value, context) => {
              dataAssignmentsFromTemplateExecution[identifier] = value.ToObjectValue();
              return value;
           }
      };
      var result = await template.RenderAsync(context);
      Assert.Equal("b", dataAssignmentsFromTemplateExecution["a"]);
      Assert.Equal("d", dataAssignmentsFromTemplateExecution["c"]);
      Assert.Equal(2, dataAssignmentsFromTemplateExecution.Count);
  }

[sebastienros]

@deanebarker I understand, but since we are there I prefer to make it complete and not have someone ask for the feature late, with another breaking change.

[deanebarker]

So my process of just passing the unmodified value back again is conceptually correct for what I want to do?

[sebastienros]

Yes, that's the pattern.

[deanebarker]

Great. Ship it.

[sebastienros]

You could write your own extension method like this to have the same pattern as you had initially, while using the overly complicated solution I came up with:

public static TemplateContext OnAssigned(this TemplateContext self, Action<string, FluidValue> assigned))
{
    self.Assigned = (indentifier, value, context) => 
    {
        assigned(identifier, value);
        return ValueTask.FronmResult<FluidValue>(value);
    };
}

[deanebarker]

You mean...complicate it further to avoid complication? ... 😀

[sebastienros]

Every programmer should take some philosophy classes.

[deanebarker]

"I think, therefore I am... going to over-engineer this for no reason."

[hishamco]

I'm not sure why you split into two delegates and why the signature is the same

[deanebarker]

Honestly, I don't quite get this either. Whether you use assign or capture, it's the same basic idea, conceptually.