# vec_type2.tbl_df

##### Find the common type for a pair of vector types

`vec_type2()`

finds the common type for a pair of vectors, or dies trying.
It forms the foundation of the vctrs type system, along with `vec_cast()`

.
This powers type coercion but should not usually be called directly;
instead call `vec_type_common()`

.

- Keywords
- internal

##### Usage

```
# S3 method for tbl_df
vec_type2(x, y)
```vec_type2(x, y)

# S3 method for logical
vec_type2(x, y)

# S3 method for integer
vec_type2(x, y)

# S3 method for double
vec_type2(x, y)

# S3 method for character
vec_type2(x, y)

# S3 method for list
vec_type2(x, y)

##### Arguments

- x, y
Either vector types; i.e.

##### Coercion rules

vctrs thinks of the vector types as forming a partially ordered set, or poset. Then finding the common type from a set of types is a matter of finding the least-upper-bound; if the least-upper-bound does not exist, there is no common type. This is the case for many pairs of 1d vectors.

The poset of the most important base vectors is shown below:
(where datetime stands for `POSIXt`

, and date for `Date`

)

##### S3 dispatch

`vec_type2()`

dispatches on both arguments. This is implemented by having
methods of `vec_type2()`

, e.g. `vec_type2.integer()`

also be S3 generics,
which call e.g. `vec_type2.integer.double()`

. `vec_type2.x.y()`

must
return the same value as `vec_type2.y.x()`

; this is currently not enforced,
but should be tested.

Whenever you implemenet a `vec_type2.new_class()`

generic/method,
make sure to always provide `vec_type2.new_class.default()`

(
which should call `stop_incompatible_cast()`

) and
`vec_type2.new_class.vctrs_unspecified()`

(which should return `x`

).

See `vignette("s3-vector")`

for full details.

*Documentation reproduced from package vctrs, version 0.1.0, License: GPL-3*