Feature: add `signal:map()` method

[b0o]

I often find myself wanting to use several different signal values in a single prop. I'm currently doing something like this:

local n = require 'nui-components'

local renderer = n.create_renderer {
  width = math.min(vim.o.columns, 64),
  height = math.min(vim.o.lines, 20),
}

local signal = n.create_signal {
  foo = false,
  bar = false,
  qux = false,
}

renderer:render(
  --
  n.rows(
    n.paragraph {
      is_focusable = false,

      -- This is the important part:
      lines = signal.foo:map(function()
        local val = signal:get_value()
        return {
          n.line(n.text('Foo: ', 'Keyword'), tostring(val.foo)),
          n.line(n.text('Bar: ', 'Keyword'), tostring(val.bar)),
          n.line(n.text('Qux: ', 'Keyword'), tostring(val.qux)),
        }
      end),

    },
    n.gap(1),
    n.columns(
      { flex = 0 },
      n.button {
        label = ' Toggle Foo ',
        autofocus = true,
        on_press = function()
          signal.foo = not signal.foo:get_value()
        end,
      },
      n.gap(1),
      n.button {
        label = ' Toggle Bar ',
        on_press = function()
          signal.bar = not signal.bar:get_value()
        end,
      },
      n.gap(1),
      n.button {
        label = ' Toggle Qux ',
        on_press = function()
          signal.qux = not signal.qux:get_value()
        end,
      }
    )
  )
)

In the above example, although I'm mapping over the foo signal value, the function seems to be called when any of the signal's values change. In fact, it seems we can map over any signal field, even if it doesn't exist, like signal.baz:map(fn).

My request: It would be nice to be able to map directly over the signal, signal:map(fn). The function fn should be called with the full value of the signal as the argument whenever any of the signal’s values change:

n.paragraph {
  is_focusable = false,
  lines = signal:map(function(val)
    return {
      n.line(n.text('Foo: ', 'Keyword'), tostring(val.foo)),
      n.line(n.text('Bar: ', 'Keyword'), tostring(val.bar)),
      n.line(n.text('Qux: ', 'Keyword'), tostring(val.qux)),
    }
  end),
},

[mobily]

Hello @b0o! For this specific case, I recommend using the combine_latest operator (I fixed it in #24). This will allow you to combine signal values from signal.foo, signal.bar, and signal.qux. Here's an example code snippet:

n.paragraph({
  is_focusable = false,
  -- This is the important part:
  lines = signal.foo:combine_latest(signal.bar, signal.qux, function(foo, bar, qux)
    return {
      n.line(n.text("Foo: ", "Keyword"), tostring(foo)),
      n.line(n.text("Bar: ", "Keyword"), tostring(bar)),
      n.line(n.text("Qux: ", "Keyword"), tostring(qux)),
    }
  end),
}),

I recommend using combine_latest instead of mapping over the signal because mapping may cause unnecessary rerenders. Feel free to let me know if you have any other questions.

[b0o]

Oh that is really cool, thank you! I think some more examples in the Signal docs would be really helpful in understanding the use-cases of the different methods, like this.