resolvers.3

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.so man.macros
.TH Tcl_AddInterpResolvers 3 8.0 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_AddInterpResolvers, Tcl_GetInterpResolvers, Tcl_RemoveInterpResolvers, Tcl_SetNamespaceResolvers, Tcl_GetNamespaceResolvers \- change the name resolution rules for commands/variables
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
void
\fBTcl_AddInterpResolvers\fR(\fIinterp, name, cmdProc, varProc, compiledVarProc\fR)
.sp
int
\fBTcl_GetInterpResolvers\fR(\fIinterp, name, resInfoPtr\fR)
.sp
int
\fBTcl_RemoveInterpResolvers\fR(\fIinterp, name\fR)
.sp
void
\fBTcl_SetNamespaceResolvers\fR(\fInamespacePtr, cmdProc, varProc, compiledVarProc\fR)
.sp
int
\fBTcl_GetNamespaceResolvers\fR(\fInamespacePtr, resInfoPtr\fR)
.SH ARGUMENTS
.AS Tcl_ResolveCompiledVarProc *compiledVarProc
.AP Tcl_Interp *interp  in
Interpreter whose name resolution rules are being queried or modified.
.AP char *name in
Name for a group of name resolution procedures.
.AP Tcl_ResolveCmdProc *cmdProc in
Procedure which will be used to resolve command names.
.AP Tcl_ResolveVarProc *varProc in
Procedure which will be used to resolve variable names at run time.
.AP Tcl_ResolveCompiledVarProc *compiledVarProc in
Procedure which will be used to resolve variable names at compile time.
.AP Tcl_ResolverInfo *resInfoPtr out
Returns the resolution procedures that are currently in effect for
a particular namespace or for a particular name resolution scheme
in the interpreter.
.AP Tcl_Namespace *namespacePtr in
Namespace whose name resolution rules are being queried or modified.
.BE

.SH DESCRIPTION
.PP
These procedures make it possible to change the way that Tcl
resolves command/variable names.  The name resolution rules are
changed by supplying three procedures:  \fIcmdProc\fR, \fIvarProc\fR, and
\fIcompiledVarProc\fR.  See the section \fBHOW NAME RESOLUTION PROCEDURES
WORK\fR for details about these procedures.
.PP
The name resolution rules can be changed for a particular namespace,
for an entire interpreter, or both.  When a name needs to be resolved,
Tcl handles it as follows.  The name resolution scheme for the
current namespace is consulted first.  Each of the name resolution
schemes for the interpreter are consulted next.  Finally, Tcl uses
the default rules for name resolution as described for the
\fBnamespace\fR command.
.PP
\fBTcl_AddInterpResolver\fR adds a set of name resolution procedures
to an interpreter.  The procedures are identified by a string \fIname\fR,
so they can be queried or deleted later on.  All of the name resolution
schemes for the interpreter are kept on a list, and they are consulted
in order from most- to least-recently added.  For example, suppose one
extension adds a name resolution scheme called "fred", and another
extension adds another scheme called "barney".  When a name is resolved,
the "barney" scheme will be consulted first, followed by the "fred"
scheme, if necessary.
.PP
\fBTcl_GetInterpResolver\fR looks for a particular name resolution
scheme in an interpreter.  If the \fIname\fR is recognized, this
procedure returns a non-zero value along with pointers to the
name resolution procedures in the \fIresInfoPtr\fR structure.  Otherwise,
the procedure returns 0.
.PP
\fBTcl_RemoveInterpResolver\fR looks for a particular name resolution
scheme in an interpreter.  If the \fIname\fR is recognized, this
procedure deletes the scheme and returns a non-zero value.  Otherwise,
it returns 0.
.PP
\fBTcl_SetNamespaceResolver\fR sets the name resolution procedures
for a particular namespace.  Unlike an interpreter, a namespace can
have only one name resolution scheme in effect at any given time.
.PP
\fBTcl_GetNamespaceResolver\fR returns the name resolution procedures
for a particular namespace.  If the namespace has a special name
resolution scheme, this procedure returns a non-zero value along
with pointers to the name resolution procedures in the \fIresInfoPtr\fR
structure.  Otherwise, the procedure returns 0.
.SH "HOW NAME RESOLUTION PROCEDURES WORK"
A name resolution scheme is enforced by three name resolution procedures.
The \fIcmdProc\fR procedure is used to resolve command names.  It must
conform to the following type:
.CS
typedef int Tcl_ResolveCmdProc(Tcl_Interp* \fIinterp\fR,
        char* \fIname\fR, Tcl_Namespace* \fIcontext\fR, int \fIflags\fR,
        Tcl_Command* \fIrPtr\fR);
.CE
The \fIinterp\fR argument is the interpreter performing the resolution;
\fIname\fR is the command name being resolved; \fIcontext\fR is the
namespace context containing the command reference; and \fIflags\fR
may contain TCL_LEAVE_ERR_MSG.
.PP
If this procedure recognizes the command \fIname\fR, it should
store the Tcl_Command token for that command in the \fIrPtr\fR
argument and return TCL_OK.  If this procedure doesn't recognize
the command \fIname\fR, it should return TCL_CONTINUE, and the
name resolution will continue with another procedure or with the
default Tcl resolution scheme.  If this procedure recognizes
the command \fIname\fR, but for some reason the command is
invalid, the procedure should return TCL_ERROR.  If the \fIflags\fR
argument contains TCL_LEAVE_ERR_MSG, the procedure should leave
an error message in the interpreter, explaining why the command
is invalid.
.PP
The \fIvarProc\fR procedure is similar to \fIcmdProc\fR, but it is
used to resolve variable names encountered at run time.  It must
conform to the following type:
.CS
typedef int Tcl_ResolveVarProc(Tcl_Interp* \fIinterp\fR,
        char* \fIname\fR, Tcl_Namespace* \fIcontext\fR, int \fIflags\fR,
        Tcl_Var* \fIrPtr\fR);
.CE
The \fIinterp\fR argument is the interpreter performing the resolution;
\fIname\fR is the variable name being resolved; \fIcontext\fR is the
namespace context containing the variable reference; and \fIflags\fR
may contain TCL_GLOBAL_ONLY, TCL_NAMESPACE_ONLY, or TCL_LEAVE_ERR_MSG.
.PP
If this procedure recognizes the variable \fIname\fR, it should
store the Tcl_Var token for that variable in the \fIrPtr\fR
argument and return TCL_OK.  If this procedure doesn't recognize
the variable \fIname\fR, it should return TCL_CONTINUE, and the
name resolution will continue with another procedure or with the
default Tcl resolution scheme.  If this procedure recognizes
the variable \fIname\fR, but for some reason the variable is
not accessible, the procedure should return TCL_ERROR.  If the
\fIflags\fR argument contains TCL_LEAVE_ERR_MSG, the procedure
should leave an error message in the interpreter, explaining why
the variable reference is invalid.
.PP
Note that this procedure should look for the TCL_GLOBAL_ONLY and
TCL_NAMESPACE_ONLY flags.  It should handle them appropriately, or
return TCL_CONTINUE and let Tcl handle the reference.  But it should
not ignore the flags.
.PP
Tcl also resolves variables when a body of code is compiled; the
\fIcompiledVarProc\fR procedure handles that case.  It must
conform to the following type:
.CS
typedef int Tcl_ResolveCompiledVarProc(Tcl_Interp* \fIinterp\fR,
        char* \fIname\fR, int \fIlength\fR, Tcl_Namespace* \fIcontext\fR,
        Tcl_ResolvedVarInfo* \fIrPtr\fR);
.CE
The \fIinterp\fR argument is the interpreter performing the resolution;
\fIname\fR is the variable name being resolved; \fIlength\fR is the
number of bytes in \fIname\fR, which is not a null-terminated
string; and \fIcontext\fR is the namespace context containing the
variable reference.
.PP
If this procedure recognizes the variable \fIname\fR, it should
return some information characterizing the variable in the
\fIrPtr\fR structure.  This structure is defined as follows:
.CS
typedef struct Tcl_ResolvedVarInfo {
    ClientData \fIidentity\fR;
    Tcl_ResolveRuntimeVarProc *\fIfetchProc\fR;
    Tcl_ResolveVarDeleteProc *\fIdeleteProc\fR;
} Tcl_ResolvedVarInfo;
.CE
The \fIidentity\fR field is an arbitrary value that characterizes
the variable.  Each variable should have a unique identity.  Each
time the compiled code is executed, Tcl will call the \fIfetchProc\fR
procedure to get the actual variable for a particular \fIidentity\fR
value.  This callback procedure must conform to the following type:
.CS
typedef Tcl_Var Tcl_ResolveRuntimeVarProc(Tcl_Interp* \fIinterp\fR,
    ClientData \fIidentity\fR);
.CE
The \fIfetchProc\fR procedure takes the \fIinterp\fR interpreter
and the \fIidentity\fR from compile time and returns a Tcl_Var
token representing the variable.  If for some reason the variable
can't be found, this procedure should return NULL, and Tcl will
create a local variable within the call frame of the procedure
being executed.
.PP
When the compiled code is discarded, Tcl calls the \fIdeleteProc\fR
procedure to release the \fIidentity\fR data.  The delete procedure
must conform to the following type:
.CS
typedef void Tcl_ResolveVarDeleteProc(ClientData \fIidentity\fR);
.CE
.PP
In general, the \fIvarProc\fR and \fIcompiledVarProc\fR procedures
should \fIboth\fR be defined.  If the \fIcompiledVarProc\fR is not
defined, then Tcl will create local variables for any variable
names that are not recognized within a procedure.  If the \fIvarProc\fR
is not defined, then Tcl will not recognize variables that are
encountered at runtime.  For example, consider the following procedure:
.CS
proc foo {args} {
    set anotherRef "1"
    set name "another"
    set ${name}Ref "2"
}
.CE
Suppose that the \fIcompiledVarProc\fR resolves the name
\fBanotherRef\fR at compile time.  The name \fB${name}Ref\fR
can't be resolved at compile time, so the resolution of that
name is deferred to run time.  If the \fIvarProc\fR procedure
must intercept the name \fBanotherRef\fR at run time and
supply the appropriate variable.

.SH KEYWORDS
interpreter, namespace, resolution