:sig
function u64(value : as string, opt : dval = {}) u64

:params
value : scalar value or text to convert
opt : options map with `fallback` and `base`

:returns
A converted `u64`, or `opt.fallback`.

:content
`u64()` converts the exact text from `value`. It uses base 10 unless `opt.base` selects another integer base. `opt.fallback` is the result for empty text or text that does not parse. It defaults to `0`.

`value` accepts scalar values through `as string`. The conversion keeps scalar text exact. Empty and missing `dval` values both convert to empty text. Use `value?` before conversion when presence matters. An empty value is present, but a missing value is not.

`u64(dval(true))` now returns the fallback. `true` converts to the text `"true"`, which is not a number.

The options map accepts only `fallback` and `base`. An unknown key is an error.

:example capy render
print(u64("2a", base: 16, fallback: 99), "\n")

:see-group
constructors
