iostream.stream.readobject

Deserializes an object from the stream

Parameters

Return value

The value writeobject encoded: null, a bool, an int, a float, a string, an array, a table, or an instance of a class named in classes. Building an instance calls that class's constructor and then its __setstate method with the saved state.

Errors

Throws Unexpected end of data during deserialization when the stream runs out of bytes before a complete value has been read, including when nothing is left, and Invalid start marker during deserialization or Invalid end marker during deserialization when the bytes at the cursor are not what writeobject produces, for example a stream not created by it, or one read from the wrong position.

An instance in the data needs classes to resolve it, and that class needs a __setstate method to receive the saved state:

• Instance found during deserialization, but available classes not set or not a table - classes is missing or not a table
• Class not found in available classes during deserialization - classes does not have the serialized class's name as a key
• Class must have __setstate method for deserialization - the class has no __setstate

Notes

The same method works on a file. Pairing writeobject and readobject on the same stream round-trips a value, provided classes lists every class either side needs; see iostream.stream.writeobject for what it can encode.

Example

from "iostream" import blob

let b = blob(0)
b.writeobject(42)
b.seek(0)
println("b.readobject() =", b.readobject()) // 42

let empty = blob(0)
try { empty.readobject() } catch (e) { println("empty.readobject() throws:", e) } // nothing was ever written

class Point { function __getstate() { return 1 } function __setstate(s) {} }
let b2 = blob(0)
b2.writeobject(Point(), {Point=Point})
b2.seek(0)
try { b2.readobject() } catch (e) { println("b2.readobject() throws:", e) } // classes omitted this time

b.readobject() = 42
empty.readobject() throws: Unexpected end of data during deserialization
b2.readobject() throws: Instance found during deserialization, but available classes not set or not a table

See also