# lerp static method Null safety

- BorderRadiusGeometry? a,
- BorderRadiusGeometry? b,
- double t

Linearly interpolate between two BorderRadiusGeometry objects.

If either is null, this function interpolates from BorderRadius.zero, and the result is an object of the same type as the non-null argument. (If both are null, this returns null.)

If lerp is applied to two objects of the same type (BorderRadius or BorderRadiusDirectional), an object of that type will be returned (though this is not reflected in the type system). Otherwise, an object representing a combination of both is returned. That object can be turned into a concrete BorderRadius using resolve.

The `t`

argument represents position on the timeline, with 0.0 meaning
that the interpolation has not started, returning `a`

(or something
equivalent to `a`

), 1.0 meaning that the interpolation has finished,
returning `b`

(or something equivalent to `b`

), and values in between
meaning that the interpolation is at the relevant point on the timeline
between `a`

and `b`

. The interpolation can be extrapolated beyond 0.0 and
1.0, so negative values and values greater than 1.0 are valid (and can
easily be generated by curves such as Curves.elasticInOut).

Values for `t`

are usually obtained from an Animation<double>, such as
an AnimationController.

## Implementation

```
static BorderRadiusGeometry? lerp(BorderRadiusGeometry? a, BorderRadiusGeometry? b, double t) {
assert(t != null);
if (a == null && b == null) {
return null;
}
a ??= BorderRadius.zero;
b ??= BorderRadius.zero;
return a.add((b.subtract(a)) * t);
}
```