# bin/set-f64-le
Return a copy of `$bytes` with a 64-bit float written at `offset`
(little-endian).
Byte strings are immutable — the original `$bytes` is unchanged.
## Syntax
[bin/set-f64-le $bytes $offset $value]
## Parameters
- `$bytes` — byte string to copy and write into
- `$offset` — 0-based byte offset
- `$value` — value to write (cast to the 64-bit float width)
## Examples
def buf [bin/set-f64-le [bin/zeros 8] 0 3.25] [bin/f64-le-at $buf 0] # → 3.25
## Returns
New byte string. A negative or out-of-bounds offset returns `%Err{:message}`.
## See Also
`bin/f64-le-at`, `bin/set-f64-be`, `bin/set-bytes`, `bin/bytes`