Chapter 6: Arrays

Question 1

What are the design issues for arrays?

Answer 1

Issues include
- legal subscript types
- range checking of subscripts
- when are subscript ranges bound?
- when does array allocation take place?
- are ragged or rectangular multidimensioned arrays allowed, or both?
- allowed slice types.

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Question 2

Define static, fixed stack-dynamic, stack-dynamic, fixed heap-dynamic, and heap-dynamic arrays. What are the advantages of each?

Answer 2

Static: Subscript ranges and storage are bound before run time. Advantage: Efficiency (no dynamic allocation).

Fixed stack-dynamic: Storage is allocated at declaration time, but size is static. Advantage: Space efficiency.

Stack-dynamic: Range and storage are bound dynamically at run time. Advantage: Flexibility.

Fixed heap-dynamic: Subscript ranges and storage binding are fixed after allocation from the heap. Advantage: Flexibility (size fits the problem).

Heap-dynamic: Subscript ranges and storage allocation can change during execution. Advantage: Maximum flexibility.

Question 3

What happens when a nonexistent element of an array is referenced in Perl?

Answer 3

It yields undef, but no error is reported.

Question 4

What languages support negative subscripts?

Answer 4

Ruby, Lua, and Perl.

Question 5

What languages support array slices with stepsizes?

Answer 5

Python.

Question 6

What array initialization feature is available in Ada that is not available in other common imperative languages?

Answer 6

Ada allows initializing specific indices directly using the arrow operator => and an others clause for remaining elements.

Question 7

What is an aggregate constant?

Answer 7

A parenthesized list of values used to initialize an array.

Question 8

What array operations are provided specifically for single-dimensioned arrays in Ada?

Answer 8

Catenation (specified by &).

Question 9

Define row major order and column major order.

Answer 9

Row major: Elements are stored by rows (first subscript varies slowest).
Column major: Elements are stored by columns (last subscript varies slowest).

Question 10

What is an access function for an array?

Answer 10

It is a mapping from the array name and set of subscript values to the address of an element.

Question 11

What are the required entries in a Java array descriptor, and when must they be stored?

Answer 11

It requires the fixed maximum length and current length, stored at run time (because Java arrays are fixed heap-dynamic).

Question 12

What is the structure of an associative array?

Answer 12

It is an unordered collection of data elements indexed by an equal number of keys (each element is a key-value pair).

Question 13

How does JavaScript support sparse arrays?

Answer 13

JavaScript supports sparse arrays by treating them as objects containing specific items, not as a reserved block of empty space.