What ⇸ means
It marks a function that may leave some inputs without an output.
Z notation is a formal language for specifying computing systems. There, ⇸ is the partial function arrow (also called the partial map arrow): some elements of the stated input set may have no output. By contrast, → marks a total function, which has an output for every element of its domain.
Z notation took shape in the late 1970s. Other arrow conventions have separate histories: a limit arrow was introduced in 1905 and became widespread in books by 1908. By 1936, → was used to map individual elements. Those dates describe different arrow conventions.
Specialist mathematical notation; read it within a system that defines it.
The stroke does not mean “blocked” on its own.
Don't confuse it with
3Questions people ask
1Why does ⇸ look different in different fonts?
The font draws this text character, so the arrowhead, spacing, or stroke proportions may vary. At small sizes, a faint vertical stroke can make it look like a plain right arrow.
How to type ⇸
⇸\21F8Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.