objc:data

(objc:data buffer)

An NSMutableData holding the buffer's bytes. buffer is a packed float array of any rank (single-float, 4 bytes an element; double-float, 8), a packed (unsigned-byte 8|16|32) vector, or a string (its UTF-8 bytes). The bytes are exactly what write-sequence would write for the same buffer -- little-endian, row-major -- so a #f matrix reaches a GPU vertex buffer with no conversion step in between.

This is how a block of memory crosses into Objective-C: [data bytes] answers the address a void * parameter wants, [data mutableBytes] is writable scratch a callee can fill, and objc:bytes reads the result back. Part of the macOS-only objc package -- the interpreter (java -jar, or the rontolisp native binary) and a compiled .class / .jar, never a .wasm; on a machine without the runtime it signals an error. See the macOS GUI guide.

CL-USER> (objc:send (objc:data "hello") "length")
5
CL-USER> (objc:bytes (objc:data (make-array 2 :element-type 'single-float :initial-contents '(1.0 2.0))))
#(0 0 128 63 0 0 0 64)