Package: Kernel-Methods

Class: BlockClosure

Introduction

Environment: container

• Contains a sequence of operations

• Defined by Mindscript expressions inside square brackets

• Permits to defer the enclosed operations until a variant of #value is executed

• Can have its own arguments and temporaries as a regular method but it also has the ability to use external variables

• It has enclosing method or block temporaries, arguments, and receiver.

Some message needs a code block as argument. For example, #do: needs a block to be executed for each element of the receiver.

The block is executed with the element as argument.

{1. 2. 3. 4. 5. 6. 7. 8. 9. 10} do: [:each | Console print: each, '. '].

You can also use a local variable in a block:

{1. 2. 3. 4. 5. 6. 7. 8. 9. 10} do: [:each |
  | sum |
  sum := 10 + each.
  Console print: sum, '. '].

We can also use the block as a local variable, and execute it later by sending value to it, or value: with an argument.

aBlock := [ Console print: 'Hello world' ].
"Execute a block"
aBlock value.

"Execute a block with an argument"
aBlock := [:each | Console print: each, '. '].
{1. 2. 3. 4. 5. 6. 7. 8. 9. 10} do: [ :item | aBlock value: item].

Instance Method

Category: accessing

• asString - answer the code string of this block closure.

• numArgs - answer the number of arguments of the receiver.

Category: controlling

• whileFalse: - Ordinarily compiled in-line, and therefore not overridable. This is in case the message is sent to other than a literal block. Evaluate the argument, aBlock, as long as the value of the receiver is false.

  For example:

  i := 1.
  [ i > 10 ] whileFalse: [ Console print: i, '. '.
    i := i + 1 ].

• whileTrue: - Ordinarily compiled in-line, and therefore not overridable. This is in case the message is sent to other than a literal block. Evaluate the argument, aBlock, as long as the value of the receiver is true.

  For example:

  i := 1.
  [ i <= 10 ] whileTrue: [ Console print: i, '. '.
    i := i + 1 ].

Category: evaluating

• ensure: - Evaluate a termination block after evaluating the receiver, regardless of whether the receiver's evaluation completes.

• onErrorDo: - Evaluate an error handling block when there is an exception when evaluating the receiver.

  For example, we can use onErrorDo: to handle an error when divide by zero.

  
  a := 1.
  aBlock := [ a := a / 0 ].
  
  aBlock onErrorDo: [ :ex | a := 0].

• value - Evaluate the receiver and answer the result.

• value: - Evaluate the receiver with the given argument and answer the result.

• value:value: - Evaluate the receiver with the given arguments and answer the result.

• value:value:value: - Evaluate the receiver with the given arguments and answer the result.

• value:value:value:value: - Evaluate the receiver with the given arguments and answer the result.