docs/pdds/pdd02_vtables.pod - Common vtable format for all variables
This PDD presents the vtable entries, and their order, that all variables MUST provide.
All parrot variables hide their guts behind a magic parrot structure generally referred to as a PMC, or Parrot Magic Cookie. Nothing outside the core of parrot (in fact, nothing outside the data type's vtable routines) should infer anything about a PMC (hence the Magic part).
The first parameter to any vtable routine should be the current interpreter. The second parameter should be the PMC itself.
vtables are neat because they decouple the interface and implementation of various object functions. This does mean, though, that you need to either know what functions are available and what they do, or have some method of finding out. It's faster if you know which vtable entry does what, so that's the method parrot's using.
The actual vtable structure contains pointers to functions that implement the methods for that particular vtable. All pointers must point to valid functions with appropriate prototypes.
This is a list of each of the vtable methods, their prototypes, and a description of the method.
The following functions are singleton functions. (There are no keyed versions of these)
The init vtable method takes an unused PMC as a parameter and turns it into a PMC appropriate for the class owning the vtable. Called as a class method. There is also a form that accepts a PMC initializer as a third argument.
This form of the init method takes a single initializer parameter. The initializer is an array that contains keys and values. The meaning of the keys and their corresponding values is left up to the PMC.
Keys are either strings or integers. If strings, the PMC is responsible for figuring out what the string represents. If integers, it means the meaning has been pre-figured based on meta-information from the class.
For example, if a class has the known properties "Size", "Dimension" and "Color", they may be assigned the values 100, 101, and 102. If the creator of the PMC knows enough about the class to make the translation to numbers it may; otherwise, the raw strings may be used. So, for the declaration:
my @foo Size(12), Dimension(3), Color("Green");
the init array may be [100, 12, 101, 3, 102, "Green"] or ["Size", 12, "Dimension", 3, "Color", "Green"]. Note that, in all cases, the array is an array of PMCs. (So you get either an int PMC or a string PMC in the list of keys).
XXX: what does this do?
Turn the PMC into a PMC of type type. If the morphing can't be done in any reasonable way -- for instance if an integer is asked to turn into an Array -- then the PMC is first destroyed, then recreated as an empty PMC of the new type.
type
This method is primarily used when the interpreter has need of coercing a PMC to a particular type, and isn't meant as a general purpose casting tool. Compilers should only emit valid transformations.
Called by the DOD when it is sweeping through the PMCs and has detected that this PMC is both alive and has a custom mark routine (as indicated by the custom mark PMC flag).
If a PMC has this flag set, then it is responsible for marking all buffers and PMCs under its control as alive. If it does not, those PMCs or buffers may be collected later. This method does not have to call the mark method on any PMCs it marks--the DOD system takes care of that. (So no need to recurse into aggregate PMCs or anything of the sort).
mark
This method may allocate no memory from Parrot, nor may it alter Parrot's internal structures. It should have no side-effects from the C level either.
This routine may not throw an exception.
This method is called by the DOD when it determines that a PMC is dead and that the PMC has marked itself as having a destroy method.
When this method finishes, the PMC will be marked as dead. As such you should make sure that you do not leave any references to it in any parrot structure by the end of the method.
This method may not throw an exception. It will be ignored if it does.
Return the value from the property hash of self keyed by key. The key should not be NULL.
Set the value in the property hash of self that is keyed by key to the value of value. The key should not be NULL.
Delete the value from the property hash of self keyed by key. The key should not be NULL.
Return the entire property hash for self.
The following functions have a plain form, a _keyed form, and a _keyed_int form. The keyed forms take a PMC* or INTVAL for each PMC parameter. The PMC* parameter for each PMC is NULL if there is no key for that PMC; this means that that argument is unkeyed.
In some cases, the caller must provide a non-NULL key. Those cases are explicitly stated below. In the other cases, you may have to implement the keyed vtable methods and check for a NULL self key even if you are implementing a non-aggregate type. If the self key is non-NULL and the PMC class is a non-aggregate type, the _keyed_* methods should throw an exception.
If you do not implement the _keyed_int methods, the default will convert the INTVAL into a key PMC* and call the corresponding _keyed method.
The keyed methods should NOT assume that the key pointer will be valid after the method exits. The pointer may be to a stack variable in the calling function.
Return the type of the PMC. Type is a unique tag associated with the PMC when the PMC's class is loaded. Negative numbers are considered interpreter-specific, non-public types.
Return the type of the PMC indexed by key. The key parameter is guaranteed not to be NULL for this method.
Return the subtype of a PMC. (Note that this may be unimplemented, and may go away). This is intended to return information about the PMC--what type of number or string it is, whether it's a scalar, hash, array, or list, and suchlike things.
Return the name of the class for the PMC.
Return a clone of yourself.
Return a subroutine PMC for the passed method name. This subroutine PMC may be cached, so the method must return an equivalent sub PMC each time, or be capable of dealing with the returned sub PMCs being reused.
Return the native integer value of the PMC.
Return the native integer value of the PMC indexed by key. The key parameter is guaranteed not to be NULL for this method.
Return the native floating-point value of the PMC.
Return the native floating-point value of the PMC indexed by key. The key parameter is guaranteed not to be NULL for this method.
Return the value of the PMC as a new bignum PMC.
Return the native string value of the PMC. This may be in the encoding of the PMC's choice.
Return the string value of the PMC indexed by key. The key parameter is guaranteed not to be NULL for this method.
Return the constant TRUE if the PMC is true, or FALSE if the PMC is false. The definition of truth for a given PMC will depend on the type of the PMC: for a scalar, it may be as simple as 0 or "" being false, and any other value being true.
Return the PMC for this PMC. While this may seem nonsensical, it's useful in several circumstances. If the thing being accessed may return something odd, for example a reference, it may return a value different from the PMC that get_pmc is being called on.
Return the PMC indexed by key. The key parameter is guaranteed not to be NULL for this method.
Return a pointer to some data. The details of the data (type, location etc.) depend on the PMC.
Sets the PMC to the integer value passed.
Sets the PMC to the integer value of the PMC in value. In this case, value is guaranteed to be of the same type as self so optimizations may be made.
Sets the PMC indexed by key to the integer value passed in value. The key parameter is guaranteed not to be NULL for this method.
Sets the PMC to the floating-point value passed.
Sets the PMC to the floating-point value of the PMC in value. In this case, value is guaranteed to be of the same type as self so optimizations may be made.
Sets the PMC indexed by key to the floating-point value passed in value. The key parameter is guaranteed not to be NULL for this method.
Morph the PMC to a BIGNUM PMC with value being the passed in value.
Sets the PMC to the passed in string value.
Sets the PMC to the copied string value.
Sets the PMC to the string value of value. In this case, value is guaranteed to be of the same type as self so optimizations may be made.
Sets the PMC indexed by key to the string value passed in value. The key parameter is guaranteed not to be NULL for this method.
Sets the boolean state of the PMC to TRUE if value is TRUE, or FALSE if value is FALSE.
Make the PMC self refer to the PMC value.
Sets the value of the PMC in self to the value of the PMC in value by copying the value.
Sets the value of the PMC keyed by key to the value of the PMC in value.
Sets a pointer inside the PMC. The details depend on the PMC.
Return the number of elements in the PMC.
Return the integer value of the last item on the list, removing that item.
Return the floating-point value of the last item on the list, removing that item.
Return the string value of the last item on the list, removing that item.
Return the PMC value of the last item on the list, removing that item.
Add the passed in integer value to the end of the list.
Add the passed in floating-point number to the end of the list.
Add the passed in string to the end of the list.
Add the passed in PMC to the end of the list.
Return the integer value of the first item on the list, removing that item.
Return the floating-point value of the first item on the list, removing that item.
Return the string value of the first item on the list, removing that item.
Return the PMC value of the first item on the list, removing that item.
Add the passed in integer value to the beginning of the list.
Add the passed in floating-point number to the beginning of the list.
Add the passed in string to the beginning of the list.
Replace the count PMCs at offset offset from the beginning of self with the PMCs in the aggregate value.
Add self to value and store the result in dest. Note that dest may be equal to self; in that case optimizations may be made.
If dest is NULL create a result PMC of an appropriate type. Subtract value from self and store the result in dest. Note that dest may be equal to self; in that case optimizations may be made.
Inplace operation self -= value.
Multiply value by self and store the result in dest. Note that dest may be equal to self; in that case optimizations may be made.
Divide self by value and store the result in dest. Note that dest may be equal to self; in that case optimizations may be made.
Divide self by value and store the remainder in dest. Note that dest may be equal to self; in that case optimizations may be made.
Note: modulus uses the Knuth's "corrected mod" algorithm, as implemented in src/utils.c, while cmodulus uses the C-style fmod function.
modulus
cmodulus
Negate the sign of self and store the result in dest. Note that self and dest may refer to the same PMC, in which case optimizations may be made.
Calculate the bitwise-OR of self and value and store the result in dest. Note that dest may be equal to self; in that case optimizations may be made.
Calculate the bitwise-AND of self and value and store the result in dest. Note that dest may be equal to self; in that case optimizations may be made.
Calculate the bitwise-XOR of self and value and store the result in dest. Note that dest may be equal to self; in that case optimizations may be made.
Calculate the bitwise-OR of the strings in self and value and store the result in dest. Note that dest may be equal to self; in that case optimizations may be made.
Calculate the bitwise-AND of the strings in self and value and store the result in dest. Note that dest may be equal to self; in that case optimizations may be made.
Calculate the bitwise-XOR of the strings in self and value and store the result in dest. Note that dest may be equal to self; in that case optimizations may be made.
Apply a bitwise negation to self and store the result in dest. Note that self and dest may refer to the same PMC; in that case optimizations may be made.
Apply a leftward shift of value bits to the number stored in self, and place the resulting value in dest. Note that self and dest may refer to the same PMC; in that case optimizations may be made.
Applies a rightward shift of value bits to the number stored in self, and places the resulting value in dest. Note that self and dest may refer to the same PMC; in that case optimizations may be made.
Concatenate the strings in self and value and store the result in dest. Note that self and dest may refer to the same PMC; in that case optimizations may be made.
Return TRUE if the two PMCs are generically equivalent, or FALSE if they aren't.
Return TRUE if the PMCs are the same, and FALSE if they're not. In this case, "the same" means identical at a low level. For plain equality, use the is_equal method.
Compare the two PMCs as PMCs (whatever that means for the class). Return -1 if self is smaller, 0 if the two are equal, and 1 if value is smaller.
Compare the two PMCs numerically. Return -1 if self is smaller, 0 if the two are equal, and 1 if value is smaller.
Compare the two PMCs as strings. Return -1 if self is smaller, 0 if the two are equal, and 1 if value is smaller.
Do a short-circuiting logical-OR of self and value, storing the winner in dest.
Do a short-circuiting logical-AND of self and value, storing the winner in dest.
If exactly one of self or value is true, store it in dest. Else set dest to be false.
Do a logical-NOT on self and stores the result in dest.
Repeat the string value of self value times and store the resultant string in dest.
Auto-increment the PMC.
Auto-decrement the PMC.
Set dest to the absolute value of SELF. Note: dest may be SELF.
dest
SELF
Only valid for keyed access.
Returns TRUE if the key exists in the aggregate being queried; otherwise, return FALSE.
The key is guaranteed to be non-NULL.
Check to see if the PMC is defined. Return TRUE if it is; otherwise, return FALSE.
Return TRUE if the value of self keyed by key is defined; otherwise, return FALSE.
Delete the specified entry from the aggregate.
Given the passed in key for the PMC, return the next key.
Return a new iterator for this aggregate. The iterator should be initialized so that iterations starts at the first element of the aggregate. If the aggregate is empty, set PMC_int_val() of the iterator key to -1.
Return a new iterator for this aggregate and the given Slice key.
Place the value of the substring of self at offset offset and with length length into dest.
Return the substring of self at offset offset and with length length.
Invoke the subroutine/method in the given PMC.
It should set up the environment for the sub, and should return the location at which operation flow should continue after the subroutine returns. (Note that this will generally be the address of the next instruction).
It is NOT responsible for preserving any of the current context; the caller should have preserved anything that they want preserved before calling this method.
See pdd03_calling_conventions.pod for more details.
next* is passed in from the run loop and is the program counter of the next instruction.
Determine whether the PMC can perform the method specified by name in method. Returns TRUE if it can; otherwise, returns FALSE.
Determine whether the PMC implements the interface specified by name in method. Returns TRUE if it can; otherwise, returns FALSE.
Is the PMC a member of _class or one of its subclasses.
See also pdd15_objects.pod.
Creates a subclass, optionally with a given name.
Serialization functions.
XXX: these need documenting by somebody who understands them.
XXX: needs documenting
Maintainer: Dan Sugalski <dan@sidhe.org> Class: Internals PDD Number: 2 Version: 1.5 Status: Developing Last Modified: 27 July 2003 PDD Format: 1 Language: English
18 May 2004
1 Nov 2003
27 July 2003
22 June 2002
13 May 2002
None. First version
* Remove obsolete _keyed vtables. * s/concat_native/concat_str/
* Add set/get_pointer vtables. * Change s/KEY/PMC/ and s/INTVAL* key/INTVAL key/
Added a number of missing method definitions. Many other minor cleanups.
Many cleanups and clarifications. Much detail added. Many missing methods added.
Cleaned up the definition. It was a mess.
To install Ruby, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Ruby
CPAN shell
perl -MCPAN -e shell install Ruby
For more information on module installation, please visit the detailed CPAN module installation guide.