Make brand available as a runtime value

[indianakernick]

I'm inspecting Zod values at runtime. I've run into a situation where I would like to use branded types but I've found that the brand isn't available at runtime. The brand function takes the brand as an optional runtime parameter. I'd like this value to be stored in the type definition. This is the code that I would like to be able to write:

const schema = z.number().brand('foo');

if (schema._def.typeName === 'ZodBranded') {
  if (schema._def.brand === 'foo') {
    // ...
  }
}

I'd also like this brand property’s type to be the brand type ('foo' in the above example) if a runtime value was provided or undefined if a value wasn’t provided.

As a workaround, I might be able to get away with using the description for my use case but I need the description as a description. The brand and the description serve different purposes.

Related: #1833

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[kasper573]

I think this would be a great feature

[mpartel]

This could/would probably be used by various "Zod to X" converters that currently need the schema's name as a separate parameter.

[jpholtmeyer]

A PR for this issue has been created here: #2860

I also think this feature would be useful.
There doesn't currently seem to be an easy way to determine what 'type' a Zod object is at runtime.
Currently doing this by just checking if a unique property exists on an object by using the in operator.
This is cumbersome at times though because it occasionally requires unwrapping a Zod object to get to the shape of the business object.
Some objects also require checking a set of properties to determine uniqueness, which makes the code harder to follow.

[artalar]

I will repeat it here too: the most reliable solution is to use "unique symbol" as runtime unique markers. I mean, it would be nice if the brand will be allow to accept a symbol for both runtime and type checks.