Type inference

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Overview
Type inference: assignment by copy
Syntaxes
Operating mode
The simple types supported by the assignment by copy
Type inference: assignment by reference
Syntaxes

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Type inference

Overview

The type inference is used to simplify the declaration of variables when the variable type can be automatically deduced by the compiler. The principle is very simple. The variable type is deduced according to the value that is assigned to the variable.

The value can be assigned:

by copy.
by reference.

Type inference: assignment by copy

Syntaxes

1. Simple inference:

let <Variable> = <Value>

where:

<Variable> corresponds to the name of variable to declare.
<Value> corresponds to the value assigned to the variable to declare.

2. Multiple inference:

let (<Variable 1>, ..., <Variable N>) = (<Value 1>, ..., <Value N>)

where:

<Variable 1> ... <Variable N> correspond to the names of variables to declare.
<Value 1> ... <Value N> correspond to the values assigned to each variable to declare.

Operating mode

During the assignment by copy, if the variable type can be defined during the compilation, the variable is declared according to the type of value. A copy of value is assigned to the variable.

Examples:

let Amount = 1500.69 // real type

let City = "Montpellier" // string type

// Multiple inference
let (x, y) = (1, "A")

// Multiple inference via a procedure returning multiple values
let (x, y) = MyProcedureWithMultipleReturns()

Remark: The variable keeps its type ; its type does not change during the execution even if another value of a different type is assigned to it.

If the variable type cannot be defined during the compilation, the type will be defined during the execution, dynamically (like when a procedure parameter has no type).

For example:

// Case of unknown type during the compilation
PROCEDURE MyProc(Param1)

let MyVar = Param1

// As the Param1 parameter has no specific type,
// its type is unknown during the compilation
// The type of the Param1 variable will be based on the value passed as parameter
// during the call to the procedure.
// The MyVar variable will also have the same type
// as the type of the Param1 variable known during the execution.

The simple types supported by the assignment by copy

The simple types supported by the assignment by copy are as follows:

Type of value	Type used

boolean	boolean
unsigned integer on 1 byte	int
unsigned integer on 2 bytes	int
unsigned integer on 4 bytes	unsigned integer on 4 bytes
unsigned integer on 8 bytes	unsigned integer on 8 bytes
1-byte integer	int
2-byte integer	int
int	int
8-byte integer	8-byte integer
currency	currency
decimal	decimal
4-byte real	4-byte real
real	real
character	character
string	string (Ansi or Unicode)
string on N	string (Ansi or Unicode)
Ansi string	Ansi string
Ansi string on N	Ansi string
Unicode string	Unicode string
Unicode string on N	Unicode string
ASCIIZ string on N	Ansi string
Fixed string on N	Ansi string
Pascal string on N	Ansi string
buffer	buffer
date	date
time	time
datetime	datetime
duration	duration
font	font
procedure	procedure

Type inference: assignment by reference

Syntaxes

1. Simple inference:

let <Variable> <- <Value>

where:

<Variable> corresponds to the name of variable to declare.
<Value> corresponds to the value assigned to the variable to declare.

2. Multiple inference:

let (<Variable 1>, ..., <Variable N>) <- (<Value 1>, ..., <Value N>)

where:

<Variable 1> ... <Variable N> correspond to the names of variables to declare.
<Value 1> ... <Value N> correspond to the values assigned to each variable to declare.

The assignment by reference is available for the complex types only:

Object type: Class, Structure, .NET class, advanced type, ...
Container type: Array, Associative array, Stack, Queue, List, ...

When assigning by reference, the value of the reference variable is not copied to the new variable but the new variable points to the reference variable.

In this case, if the reference variable is modified, the new variable is also modified.

Example:

clMyClient is cClient // cClient class, clMyClient object
let clClient <- clMyClient // class type, clClient points to clMyClient object

arrPrice is array of 5 currencies
arrPrice[1] = 500.00
arrPrice[2] = 250

let tPrice <- arrPrice // array type, tPrice points to the arrPrice array