Tcl_RegisterConfig(3tcl)

✨ Tcl_RegisterConfig ✨

okay bestie, welcome to the Tcl_RegisterConfig(3tcl) page 💖 this one lives in the Tcl Library Procedures section, and it's all about registering embedded configuration info. no cap, it's short but she's important 🎀

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🌸 NAME 🌸

Tcl_RegisterConfig — procedures to register embedded configuration information ✨

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🦋 SYNOPSIS 🦋

#include <tcl.h>

Tcl_RegisterConfig(interp, pkgName, configuration, valEncoding)

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💅 ARGUMENTS 💅

• Tcl_Interp *interp (in) — points at the interpreter that the embedded config info is getting registered for. must not be NULL, fr fr, don't even try it 🙈
• const char *pkgName (in) — the name of the package that's registering the embedded configuration, as an ASCII string. which means this info is in UTF-8 too, btw. must not be NULL 😭
• const Tcl_Config *configuration (in) — points at an array of Tcl_Config entries holding the info embedded in the library. must not be NULL. the end of the array is signaled by either a key identical to NULL, or a key pointing at the empty string 🫶
• const char *valEncoding (in) — the name of the encoding used to store the configuration values, as an ASCII string. and yes, that means this info is in UTF-8 too. must not be NULL 👑

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💖 DESCRIPTION 💖

so the function we're talking about here has its base in TIP 59 ✨ and it gives extensions support for embedding configuration information right into their library, plus the ability to generate a Tcl-level interface for querying all that info. it's giving main character energy ngl 🌟

to embed configuration information into their library, an extension has to define a non-volatile array of Tcl_Config entries in one of its source files, and then call Tcl_RegisterConfig to register that info 🎀

Tcl_RegisterConfig takes four arguments:

1. a reference to the interpreter we're registering the info with
2. the name of the package registering its configuration information
3. a pointer to an array of structures
4. a string declaring the encoding used by the configuration values

the string valEncoding contains the name of an encoding that Tcl knows about. all of these names only use characters in the ASCII subset of UTF-8, so they're implicitly in the UTF-8 encoding 🌈 it's expected that keys are legible English text, and therefore using the ASCII subset of UTF-8. in other words, they're expected to be in UTF-8 too. but the values associated with the keys? those can be any string whatsoever, bestie 💜 and for those, the contents of valEncoding define which encoding was used to represent the characters of the strings.

each element of the configuration array refers to two strings containing the key and the value associated with that key 🔑 the end of the array is signaled by either an empty key or a key identical to NULL. and here's the tea: the function makes no copy of the configuration array 😳 which means the caller has to make sure that the memory holding this array is never released. that is literally the meaning behind the word non-volatile used earlier. the easiest way to pull this off is to define a global static array of Tcl_Config entries. check out the file generic/tclPkgConfig.c in the sources of the Tcl core for an example 👀

⚠️ memory warning bestie: no copy gets made, so that array has to live forever. non-volatile is not a suggestion, it's the whole vibe check 💀

when called, Tcl_RegisterConfig will:

1. create a namespace having the provided pkgName, if it doesn't already exist 🏠
2. create the command pkgconfig in that namespace and link it to the provided information, so that the keys from configuration and their associated values can be retrieved through calls to pkgconfig 🔗

the command pkgconfig will provide two subcommands, list and get:

• ::pkgName::pkgconfig list — returns a list containing the names of all defined keys 📝
• ::pkgName::pkgconfig get key — returns the configuration value associated with the specified key 🔍

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🎀 TCL_CONFIG 🎀

the Tcl_Config structure contains the following fields:

typedef struct {
    const char *key;
    const char *value;
} Tcl_Config;

she's simple, she's iconic, she does exactly what she says 💅

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⭐ KEYWORDS ⭐

embedding, configuration, library

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and that's the whole page, bestie!! 🫶 you ate this one, fr fr 💖

this was the Tcl_RegisterConfig(3tcl) manual page from Tcl 8.4 — 8.4 era Tcl core, the source of all this wisdom 🧚 go forth and register your config, you've got this 👑