How to detect the data type of an object?

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#How to detect the data type of an object?

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kaxori 03/25/2025 03:14 PM

The value of 'nested' should be detected as 'map'.
How can I achieve this ?

map := {
            "simple":"value", 
            "nested": 
              {
                "A":1,
                "B":2
              }
          }

OPkaxori

The value of 'nested' should be detected as 'map'. How can I achieve this ? ``` map := { "simple":"value", "nested": { ...

floitsch 03/25/2025 03:17 PM

You can do an is Map check

floitsch 03/25/2025 03:19 PM

Or do you mean statically?
Statically you need to use as or assign it to a typed local:

nested/Map := map["nested"]

(map["nested"] as Map)...

kaxori 03/25/2025 03:21 PM

so simple

Thank you
(die Verkalkung beginnt mit der Geburt)

kaxori 03/25/2025 03:40 PM

I searched for 'is' in Toit docs, but couldn't find anything. Neither part of language, nor part of object. How is it implemented ?

floitsch 03/25/2025 03:49 PM

Each object (except for small integers) have a class-id in their header.

floitsch 03/25/2025 03:49 PM

If you are testing for an object, a small range-check can detect whether an object is in a class-hierarchy.

floitsch 03/25/2025 03:50 PM

If you are testing for an interface, then we add is-interface methods to these classes.

floitsch 03/25/2025 03:50 PM

These methods don't actually have any code, since we just check for their existence.

floitsch 03/25/2025 03:50 PM

Integers are implemented differently: they are not actual objects, but their value shifted.

floitsch 03/25/2025 03:51 PM

So the value 3 is simply 3 << 1 == 6.

floitsch 03/25/2025 03:51 PM

To differentiate them from pointers to objects, pointers are offset by 1.

floitsch 03/25/2025 03:51 PM

So all object pointers in the Toit VM have the last bit set to 1.

floitsch 03/25/2025 03:52 PM

So is int starts by looking whether the "pointer" has 0 in the least-significant bit. If not, it also checks for the Integer class-id, which is used when values are bigger than 31 bits (since they wouldn't fit into words anymore).

floitsch 03/25/2025 03:53 PM

You can see the class-ids, by running toit tools snapshot classes my-snapshot.

kaxori 03/25/2025 03:53 PM

and is ?

floitsch 03/25/2025 03:55 PM

is

should be in there.

floitsch 03/25/2025 03:55 PM

Where does the table come from?

kaxori 03/25/2025 03:55 PM

https://docs.toit.io/language/syntax

floitsch 03/25/2025 03:55 PM

(btw: there is also is not, as in if x is not Map)

floitsch 03/25/2025 03:55 PM

I will update the table.

kaxori 03/25/2025 03:56 PM

floitsch 03/25/2025 03:56 PM

we probably missed it, because we have is and is not as operators in our parser.

floitsch 03/25/2025 03:56 PM

https://github.com/toitlang/toit/blob/1790b3c4077a06a10c9e4d271bd216a6150085a7/src/compiler/token.h#L140

toit/src/compiler/token.h at 1790b3c4077a06a10c9e4d271bd216a6150085...

Program your microcontrollers in a fast and robust high-level language. - toitlang/toit

kaxori 03/25/2025 04:02 PM

... there are a lot of muggles outside hogwarts

kaxori 03/25/2025 04:22 PM

If I try to create a composed map :

m-a := { "A":1 }
  m-b := { "B":2 } 
  m-composed := { m-a, m-b }

this way does not work. Is there a way to combine maps ?(edited)

floitsch 03/25/2025 04:23 PM

The { m-a, m-b } is a set.

floitsch 03/25/2025 04:24 PM

You can either make a list: [m-a, m-b], or a map: {"m-a": m-a, "m-b", m-b}.
Toit doesn't have JavaScript's automatic "use the variable name as key".

kaxori 03/25/2025 04:29 PM

m-composed := { m-a.first: m-a, m-b.first: m-b}

(edited)

kaxori 03/25/2025 04:31 PM

Is that the correct way to create it using the data of the 2 predefined maps ? It seems to work, but is ugly.

kaxori 03/25/2025 05:06 PM

m-composed := {:}
m-a.do: | k v |  m-composed[k] = v
m-b.do: | k v |  m-composed[k] = v

*... found another way *

floitsch 03/25/2025 05:07 PM

Yes. the second approach is nicer.

kaxori 03/25/2025 05:08 PM

I am preparing the technique to deal with maps. Goal is setup for home assistant device discovery ...

floitsch

I will update the table.

floitsch 03/26/2025 01:03 PM

Updated table is live.

kaxori 03/26/2025 01:38 PM

for those interested in maps:

map-elements := { "A":1, "B":2, "C":3 }

map := {"key":"value"}
map["k"] = "v"

// to add elements to map
map-elements.do (: |k v| map[k] = v)


map["nested"] = {:} // create "nested" sub-map
(map["nested"])["k"] = "v" // add one k-v-element to sub-map

// / to add elements to sub-map
map-elements.do (: |k v| (map["nested"])[k] = v)

sub-map := map["nested"]   // easier to read
sub-map["key"] = "value"
...

- 128 nesting levels supported !

35 messages in total