Tcl_Ensemble(3tcl)

🎀 Tcl_Ensemble(3tcl) 🎀

okay bestie, sit down, hydrate, because we're about to talk about ensemble commands — and this is the C API for them, from the Tcl library procedures. it's giving backstage pass energy. 🫶

---

✨ NAME ✨

the whole girl group, in alphabetical-ish order:

• Tcl_CreateEnsemble
• Tcl_FindEnsemble
• Tcl_GetEnsembleFlags
• Tcl_GetEnsembleMappingDict
• Tcl_GetEnsembleNamespace
• Tcl_GetEnsembleParameterList
• Tcl_GetEnsembleUnknownHandler
• Tcl_GetEnsembleSubcommandList
• Tcl_IsEnsemble
• Tcl_SetEnsembleFlags
• Tcl_SetEnsembleMappingDict
• Tcl_SetEnsembleParameterList
• Tcl_SetEnsembleSubcommandList
• Tcl_SetEnsembleUnknownHandler

— and their collective job description is literally just: manipulate ensemble commands. that's it. that's the gig. 💅

---

🌸 SYNOPSIS 🌸

#include <tcl.h>

Tcl_Command
Tcl_CreateEnsemble(interp, name, namespacePtr, ensFlags)

Tcl_Command
Tcl_FindEnsemble(interp, cmdNameObj, flags)

int
Tcl_IsEnsemble(token)

int
Tcl_GetEnsembleFlags(interp, token, ensFlagsPtr)

int
Tcl_SetEnsembleFlags(interp, token, ensFlags)

int
Tcl_GetEnsembleMappingDict(interp, token, dictObjPtr)

int
Tcl_SetEnsembleMappingDict(interp, token, dictObj)

int
Tcl_GetEnsembleParameterList(interp, token, listObjPtr)

int
Tcl_SetEnsembleParameterList(interp, token, listObj)

int
Tcl_GetEnsembleSubcommandList(interp, token, listObjPtr)

int
Tcl_SetEnsembleSubcommandList(interp, token, listObj)

int
Tcl_GetEnsembleUnknownHandler(interp, token, listObjPtr)

int
Tcl_SetEnsembleUnknownHandler(interp, token, listObj)

int
Tcl_GetEnsembleNamespace(interp, token, namespacePtrPtr)

look at her. fourteen functions, one header, zero drama. iconic. 🔥

---

💜 ARGUMENTS 💜

• Tcl_Interp *interp (in/out) — the interpreter where the ensemble is gonna be created or found. it's also where the error result messages get written, so she's doing double duty, no cap. and listen: the functions whose names start with Tcl_GetEnsemble are allowed to have a NULL for the interp, but every other function absolutely must not. do not test her. 😭
• const char *name (in) — the name of the ensemble command that's about to be created. that's the name, bestie.
• Tcl_Namespace *namespacePtr (in) — the namespace this ensemble command gets bound to. or NULL if you just want the current namespace. lowkey the lazy-girl option and we respect it.
• int ensFlags (in) — an OR'ed set of flag bits describing the basic configuration of the ensemble. rn only one bit means anything: TCL_ENSEMBLE_PREFIX. you set it when the ensemble command should also match unambiguous prefixes of subcommands. very "we'll finish your sentence" of her. ✨
• Tcl_Obj *cmdNameObj (in) — a value holding the name of the ensemble command to look up. like a little name tag but it's a Tcl_Obj. 🎀
• int flags (in) — an OR'ed set of flag bits controlling how Tcl_FindEnsemble behaves. currently only TCL_LEAVE_ERR_MSG is supported. one option, and she's serving. 💅
• Tcl_Command token (in) — a normal command token that refers to an ensemble command — or one you wanna use for testing whether it is an ensemble command in Tcl_IsEnsemble. vibe check, basically.
• int *ensFlagsPtr (out) — pointer to a variable where the current ensemble flag bits get written. currently the only bit defined is TCL_ENSEMBLE_PREFIX. 📝
• Tcl_Obj *dictObj (in) — a dictionary value used as the subcommand-to-implementation-command prefix mapping dictionary in the ensemble. may be NULL if the mapping dictionary is getting removed. bye girl 👋
• Tcl_Obj **dictObjPtr (out) — pointer to a variable where the current ensemble mapping dictionary gets written.
• Tcl_Obj *listObj (in) — a list value used for: the list of formal pre-subcommand parameters, the defined list of subcommands in the dictionary, or the unknown subcommand handler command prefix. may be NULL if the subcommand list or the unknown handler are getting removed.
• Tcl_Obj **listObjPtr (out) — pointer to a variable where the current list of formal pre-subcommand parameters, the defined list of subcommands, or the current unknown handler prefix gets written.
• Tcl_Namespace **namespacePtrPtr (out) — pointer to a variable where the handle of the namespace the ensemble is bound to gets written. she'll tell you where she lives. 🏠

---

okay that's the setup, bestie — the synopsis and every single argument, all accounted for, nothing skipped, nothing invented. more of this page is coming, so don't go anywhere. 🦋

okay bestie, part 2, let's GO — we're picking up right where we left off and honestly? this is the part where the ensemble starts spilling all its tea 💅

---

🌸 DESCRIPTION (the plot thickens) 🌸

An ensemble is a command, bound to some namespace, which consists of a collection of subcommands implemented by other Tcl commands. The first argument to the ensemble command is always interpreted as a selector that states what subcommand to execute. Like, it's the little menu at the top of the group chat and you just gotta pick your girl. 🫶

Ensembles are created using Tcl_CreateEnsemble, which takes four arguments: the interpreter to work within, the name of the ensemble to create, the namespace within the interpreter to bind the ensemble to, and the default set of ensemble flags. The result of the function is the command token for the ensemble, which may be used to further configure the ensemble using the API described below in ENSEMBLE PROPERTIES. ✨

Given the name of an ensemble command, the token for that command may be retrieved using Tcl_FindEnsemble. If the given command name (in cmdNameObj) does not refer to an ensemble command, the result of the function is NULL and (if the TCL_LEAVE_ERR_MSG bit is set in flags) an error message is left in the interpreter result. not it leaving you on read, it literally returns NULL 😭

A command token may be checked to see if it refers to an ensemble using Tcl_IsEnsemble. This returns 1 if the token refers to an ensemble, or 0 otherwise. Vibe check, basically. ✅

---

✨ ENSEMBLE PROPERTIES ✨

Every ensemble has four read-write properties and a read-only property. The properties are:

• flags (read-write) — The set of flags for the ensemble, expressed as a bit-field. Currently, the only public flag is TCL_ENSEMBLE_PREFIX which is set when unambiguous prefixes of subcommands are permitted to be resolved to implementations as well as exact matches. The flags may be read and written using Tcl_GetEnsembleFlags and Tcl_SetEnsembleFlags respectively. The result of both of those functions is a Tcl result code (TCL_OK, or TCL_ERROR if the token does not refer to an ensemble). 🎀
• mapping dictionary (read-write) — A dictionary containing a mapping from subcommand names to lists of words to use as a command prefix (replacing the first two words of the command which are the ensemble command itself and the subcommand name), or NULL if every subcommand is to be mapped to the command with the same unqualified name in the ensemble's bound namespace. Defaults to NULL. May be read and written using Tcl_GetEnsembleMappingDict and Tcl_SetEnsembleMappingDict respectively. The result of both of those functions is a Tcl result code (TCL_OK, or TCL_ERROR if the token does not refer to an ensemble) and the dictionary obtained from Tcl_GetEnsembleMappingDict should always be treated as immutable even if it is unshared. All command names in prefixes set via Tcl_SetEnsembleMappingDict must be fully qualified. 💀
• formal pre-subcommand parameter list (read-write) — A list of formal parameter names (the names only being used when generating error messages) that come at invocation of the ensemble between the name of the ensemble and the subcommand argument. NULL (the default) is equivalent to the empty list. May be read and written using Tcl_GetEnsembleParameterList and Tcl_SetEnsembleParameterList respectively. The result of both of those functions is a Tcl result code (TCL_OK, or TCL_ERROR if the token does not refer to an ensemble) and the dictionary obtained from Tcl_GetEnsembleParameterList should always be treated as immutable even if it is unshared. 🦋
• subcommand list (read-write) — A list of all the subcommand names for the ensemble, or NULL if this is to be derived from either the keys of the mapping dictionary (see above) or (if that is also NULL) from the set of commands exported by the bound namespace. May be read and written using Tcl_GetEnsembleSubcommandList and Tcl_SetEnsembleSubcommandList respectively. The result of both of those functions is a Tcl result code (TCL_OK, or TCL_ERROR if the token does not refer to an ensemble) and the list obtained from Tcl_GetEnsembleSubcommandList should always be treated as immutable even if it is unshared. 🌈
• unknown subcommand handler command prefix (read-write) — A list of words to prepend on the front of any subcommand when the subcommand is unknown to the ensemble (according to the current prefix handling rule); see the namespace ensemble command for more details. If NULL, the default behavior — generate a suitable error message — will be used when an unknown subcommand is encountered. May be read and written using Tcl_GetEnsembleUnknownHandler and Tcl_SetEnsembleUnknownHandler respectively. The result of both functions is a Tcl result code (TCL_OK, or TCL_ERROR if the token does not refer to an ensemble) and the list obtained from Tcl_GetEnsembleUnknownHandler should always be treated as immutable even if it is unshared. 🙈
• bound namespace (read-only) — The namespace to which the ensemble is bound; when the namespace is deleted, so too will the ensemble, and this namespace is also the namespace whose list of exported commands is used if both the mapping dictionary and the subcommand list properties are NULL. May be read using Tcl_GetEnsembleNamespace which returns a Tcl result code (TCL_OK, or TCL_ERROR if the token does not refer to an ensemble). bestie it's giving "you can look but you cannot touch" 👑

---

💖 REFERENCE COUNT MANAGEMENT 💖

okay this section is the ~responsible adult~ of the page, but it MATTERS, so pay attention bestie, no cap.

Tcl_FindEnsemble does not modify the reference count of its cmdNameObj argument; it only reads. Note however that this function may set the interpreter result; if that is the only place that is holding a reference to the object, it will be deleted. 😭

The ensemble property getters (Tcl_GetEnsembleMappingDict, Tcl_GetEnsembleParameterList, Tcl_GetEnsembleSubcommandList, and Tcl_GetEnsembleUnknownHandler) do not manipulate the reference count of the values they provide out; if those are non-NULL, they will have a reference count of at least 1. Note that these functions may set the interpreter result. ✨

The ensemble property setters (Tcl_SetEnsembleMappingDict, Tcl_SetEnsembleParameterList, Tcl_SetEnsembleSubcommandList, and Tcl_SetEnsembleUnknownHandler) will increment the reference count of the new value of the property they are given if they succeed (and decrement the reference count of the old value of the property, if relevant). If the property setters return TCL_ERROR, the reference count of the Tcl_Obj argument is left unchanged. Slay, consistent behavior. 💅

---

👀 SEE ALSO 👀

• namespace(3tcl)
• Tcl_DeleteCommandFromToken(3tcl)

---

🔑 KEYWORDS 🔑

command, ensemble

---

reminder bestie: getters don't bump refcounts, setters do (when they succeed), and immutability is not a suggestion, it's the law 🫶

and that's the whole page, you ATE that 💅✨ this was Tcl_Ensemble(3tcl) from Tcl 8.5 — go forth and ensemble, queen 👑💖