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Improve commentary about ArrayRef and ResTarget nodes.

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This commit is contained in:
Tom Lane
1999-07-18 03:45:01 +00:00
parent 3406901a29
commit 32664b4b4b
2 changed files with 51 additions and 18 deletions
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50
src/include/nodes/primnodes.h
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@@ -6,7 +6,7 @@
*
* Copyright (c) 1994, Regents of the University of California
*
* $Id: primnodes.h,v 1.31 1999/07/16 17:07:33 momjian Exp $
* $Id: primnodes.h,v 1.32 1999/07/18 03:45:01 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -302,13 +302,13 @@ typedef struct SubLink
/* ----------------
* Array
* arrayelemtype - base type of the array's elements (homogenous!)
* arrayelemtype - type of the array's elements (homogenous!)
* arrayelemlength - length of that type
* arrayelembyval - can you pass this element by value?
* arrayelembyval - is the element type pass-by-value?
* arrayndim - number of dimensions of the array
* arraylow - base for array indexing
* arrayhigh - limit for array indexing
* arraylen -
* arraylen - total length of array object
* ----------------
*
* memo from mao: the array support we inherited from 3.1 is just
@@ -328,15 +328,39 @@ typedef struct Array
} Array;
/* ----------------
* ArrayRef:
* refelemtype - type of the element referenced here
* refelemlength - length of that type
* refelembyval - can you pass this element type by value?
* refupperindexpr - expressions that evaluate to upper array index
* reflowerexpr- the expressions that evaluate to a lower array index
* refexpr - the expression that evaluates to an array
* refassignexpr- the expression that evaluates to the new value
* to be assigned to the array in case of replace.
* ArrayRef: describes an array subscripting operation
*
* An ArrayRef can describe fetching a single element from an array,
* fetching a subarray (array slice), storing a single element into
* an array, or storing a slice. The "store" cases work with an
* initial array value and a source value that is inserted into the
* appropriate part of the array.
*
* refattrlength - total length of array object
* refelemtype - type of the result of the subscript operation
* refelemlength - length of the array element type
* refelembyval - is the element type pass-by-value?
* refupperindexpr - expressions that evaluate to upper array indexes
* reflowerindexpr - expressions that evaluate to lower array indexes
* refexpr - the expression that evaluates to an array value
* refassgnexpr - expression for the source value, or NULL if fetch
*
* If reflowerindexpr = NIL, then we are fetching or storing a single array
* element at the subscripts given by refupperindexpr. Otherwise we are
* fetching or storing an array slice, that is a rectangular subarray
* with lower and upper bounds given by the index expressions.
* reflowerindexpr must be the same length as refupperindexpr when it
* is not NIL.
*
* Note: array types can be fixed-length (refattrlength > 0), but only
* when the element type is itself fixed-length. Otherwise they are
* varlena structures and have refattrlength = -1. In any case,
* an array type is never pass-by-value.
*
* Note: currently, refelemtype is NOT the element type, but the array type,
* when doing subarray fetch or either type of store. It would be cleaner
* to add more fields so we can distinguish the array element type from the
* result type of the subscript operator...
* ----------------
*/
typedef struct ArrayRef