Table of Contents

• 1. packedarray
  • 1.1. Syntax
  • 1.2. Stack Effects
  • 1.3. Description
  • 1.4. PostScript Level
  • 1.5. Examples
  • 1.6. Common Use Cases
    • 1.6.1. Procedure Definitions
    • 1.6.2. Read-Only Data
    • 1.6.3. Memory-Efficient Storage
  • 1.7. Common Pitfalls
  • 1.8. Error Conditions
  • 1.9. Implementation Notes
  • 1.10. Comparison with Regular Arrays
  • 1.11. See Also

1. packedarray

Creates a read-only packed array from objects on the stack (Level 2).

1.1. Syntax

any₀ ... anyₙ₋₁ n packedarray → packedarray

1.2. Stack Effects

Table 1. Before

Level	Object
n	any₀
…​	…​
1	anyₙ₋₁
0	n (number of elements)

Table 2. After

Level	Object
0	packedarray (containing any₀ through anyₙ₋₁)

1.3. Description

packedarray creates a packed array object of length n containing the objects any₀ through anyₙ₋₁ as elements. It:

1. Removes the integer n from the stack

2. Removes n objects from the stack

3. Creates a packed array containing those objects

4. Pushes the packed array on the stack

The resulting object: * Has type packedarraytype * Has the literal attribute * Has readonly access (cannot be modified) * Is more memory-efficient than regular arrays

The packed array is allocated in local or global VM according to the current VM allocation mode.

1.4. PostScript Level

Level 2 and later

1.5. Examples

Basic packed array

1 2 3 3 packedarray
% Creates read-only packed array

Storing procedures

/add /mul /sub 3 packedarray
% Packed array of operators

Mixed types

42 (text) /name 3 packedarray
% Packed array: <42 (text) /name>

1.6. Common Use Cases

1.6.1. Procedure Definitions

% In Level 2, procedure bodies are packed arrays
true setpacking
{ 1 2 add }  % Creates packed array

1.6.2. Read-Only Data

/constants 1 2 3.14159 3 packedarray def
% Constants cannot be accidentally modified

1.6.3. Memory-Efficient Storage

% Packed arrays use less memory
/data many values here n packedarray def

1.7. Common Pitfalls

Cannot Modify Packed Arrays - Packed arrays are read-only. Attempting to use put or putinterval causes [invalidaccess] error.

1 2 3 3 packedarray
dup 0 99 put  % Error: cannot modify

Global/Local VM Restrictions - If packed array is in global VM and any element is in local VM, [invalidaccess] error occurs.

Use for Procedures - In Level 2, enable packing mode with true setpacking to create packed array procedures automatically.

true setpacking
{ add mul }  % Automatically creates packed array
false setpacking

Read Operations Work Normally - Can use get, getinterval, aload, forall, etc.

1.8. Error Conditions

Error	Condition
[invalidaccess]	Packed array in global VM contains local VM objects
[rangecheck]	n is negative or exceeds implementation limit
[stackunderflow]	Fewer than n+1 objects on stack
[typecheck]	Top operand is not an integer
[VMerror]	Insufficient VM to allocate packed array

1.9. Implementation Notes

• Packed arrays typically use 50-60% less memory than regular arrays

• Elements are stored more compactly

• Created with readonly and literal attributes

• Type is packedarraytype, distinct from arraytype

• Can be used anywhere regular arrays are accepted (for read operations)

1.10. Comparison with Regular Arrays

Feature	Regular Array	Packed Array
Memory usage	More	Less (50-60% savings)
Modifiable	Yes	No (readonly)
Access speed	Slightly faster	Slightly slower
Creation	[ …​ ] or array	packedarray or procedures with packing on
Type	arraytype	packedarraytype

1.11. See Also

• array - Create regular (modifiable) array

• [ / ] - Array literal syntax

• aload - Load packed array elements

• get - Get packed array element

• forall - Iterate over packed array