---
name: "trampoline_r"
section: "3"
platform: "linux"
package: "libffcall1-dev"
version: "1.10+cvs20100619-4"
release: "Debian 9 (Stretch)"
platforms: ["linux"]
url: "https://new.carta.tech/trampoline_r"
---

# trampoline\_r(3)

closures as first-class C functions

## NAME

trampoline - closures as first-class C functions

## SYNOPSIS

**#include \<trampoline\_r.h\>**

**function = alloc\_trampoline\_r(address, data0, data1);**

**free\_trampoline\_r(function);**

```
is_trampoline_r(function)
trampoline_r_address(function)
trampoline_r_data0(function)
trampoline_r_data1(function)
```

## DESCRIPTION

These functions implement *closures* as first-class C functions. A closure consists of a regular C function and a piece of data which gets passed to the C function when the closure is called.

Closures as *first-class C functions* means that they fit into a function pointer and can be called exactly like any other C function. *function* **= alloc\_trampoline\_r(***address***,** *data0***,** *data1***)** allocates a closure. When *function* gets called, it stores in a special "lexical chain register" a pointer to a storage area containing *data0* in its first word and *data1* in its second word and calls the C function at *address*. The function at *address* is responsible for fetching *data0* and *data1* off the pointer. Note that the "lexical chain register" is a call-used register, i.e. is clobbered by function calls.

This is much like **gcc**'s local functions, except that the GNU C local functions have dynamic extent (i.e. are deallocated when the creating function returns), while *trampoline* provides functions with indefinite extent: *function* is only deallocated when **free\_trampoline\_r(***function***)** is called.

**is\_trampoline\_r(***function***)** checks whether the C function *function* was produced by a call to *alloc\_trampoline\_r*. If this returns true, the arguments given to *alloc\_trampoline\_r* can be retrieved:

**trampoline\_r\_address(***function***)** returns *address*,

**trampoline\_r\_data0(***function***)** returns *data0*,

**trampoline\_r\_data1(***function***)** returns *data1*.

## SEE ALSO

[**trampoline**(3)](/trampoline/3.md), [**gcc**(1)](/gcc/1.md), [**varargs**(3)](/varargs/3.md)

## PORTING

The way **gcc** builds local functions is described in the gcc source, file gcc-2.6.3/config/*cpu*/*cpu*.h.

## AUTHOR

Bruno Haible \<bruno@clisp.org\>

## ACKNOWLEDGEMENTS

Many ideas were cribbed from the gcc source.