---
name: "Sequence"
section: "3"
platform: "linux"
package: "objc-poc"
version: "3.1.3-2"
release: "Debian 2.2 (Potato)"
platforms: ["linux"]
url: "https://new.carta.tech/Sequence"
---

# Sequence(3)

## Sequence

**Inherits from:**

Object

## Class Description

Sequences are used to loop or  *sequence* over a group of objects.  Typically, an  **Sequence** instance is generated by using some method like  **OrdCltn** 's  **eachElement** .  Then, within a loop, one can send  **next** messages to the sequence until the end is reached (when the  **next** method returns  **nil** ).  Finally, after using the sequence, you have to free the sequence object.

## Warning

Using a sequence can lead to problems if, in sequencing over a collection, that collection is modified, e.g., as in the following :

id item;\
 id aSeq;\

aSeq = \[aCol eachElement\];\
 while ((item = \[aSeq next\])) \[aCol add:something\]; /\* WRONG !!! \*/\
 aSeq = \[aSeq free\];\

You may not modify a group of objects while sequencing over its contents.

## Method types

**Creation**

\* copy\
 \* free

**Interrogation**

\* size

**Accessing**

\* next\
 \* peek\
 \* previous\
 \* first\
 \* last

**Printing**

\* printOn:

**Performing**

\* do:

## Methods

copy

\- **copy**

Returns a copy of the sequence.  Can be used independently of the original sequence.

free

\- **free**

Frees the receiver, but not the objects in the collection being sequenced over.

size

\- ( unsigned ) **size**

Returns the total number of items in the sequence.

next

\- **next**

Returns the next object in the sequence if there is one and advances the sequence.  When it reaches the end of the sequence, returns  **nil** .

peek

\- **peek**

Returns the next object in the sequence if there is one, but does not advance the sequence.  When it reaches the end of the sequence, returns  **nil** .

previous

\- **previous**

Returns the object that was returned by the last  **next** message.  If there were no  **next** messages since the sequence was created, or the sequence is empty, returns  **nil** .  Doesn't affect the current position in the sequence.

first

\- **first**

Returns the first object in the sequence, unlesss there are no members in the sequence, in which case it returns  **nil** .  Doesn't affect the current position in the sequence.

last

\- **last**

Returns the last object in the sequence, unlesss there are no members in the sequence, in which case it returns  **nil** .  Doesn't affect the current position in the sequence.

printOn:

\- **printOn** :(IOD) *aFile*

Prints a newline separated list of the objects in the sequence to  *aFile* , by sending each individual object a  **printOn:** message.  Returns the sequence when there are no more elements left.

do:

\- **do** : *aBlock*

Performs  *aBlock* for the remaining members of a sequence.   *aBlock* should take one argument, which is the element.  Typically used as in,

\[\[aDictionary eachValue\] do:{ :each \| \[each show\]; }\];\