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General
Info

This document covers automatic type conversion rules and behavior, distinct from explicit type conversion using the cast operator.

Basic Type Conversion Rules

Type conversion is usually done in SIL allows variables of different types to be automatically converted when using the attrib assignment (=) operator between variables of different types. This page refers to the automatic type conversion, and not the one you obtain using the cast operator.

The types convertible to a target type are listed in the table below:

Target TypeConvertible typesAdditional Information / Examplesnumberstring, integer

"1" to 1

1 to 1.0

integerstring, number

"2" to 2

2.0 to 2

stringALLbooleanstring, number, integer

"true" to true

value of number != 0

datestring, number, integerConstructing a date from number assumes the number is a "to millis" representation of a dateintervalstring, number, integer

Constructing a date from number assumes the number is a "to millis" representation of an interval

60000 to "1m"

"120m" (string) to "2h" (interval)

. Type conversion occurs when you assign a value of one type to a variable of another type. The system attempts to convert the source value into a format that matches the target type while preserving the semantic meaning of the data.

To ensure correct transformation, improve code clarity and prevent unexpected behavior, make sure to:

  • Use appropriate types from the start.

  • Verify that source types can be converted to target types.

  • Verify conversion behavior with different input types.

  • For complex cases, use explicit conversions instead of relying on the automatic conversion functionality.

  • Implement proper error handling for conversion failures. This includes providing meaningful error messages.

  • Use consistent formatting in all your scripts.

Note

All conversion functionality is backward compatible with versions prior to v2.5.

Contents

Table of Contents

Basic Type Conversion Matrix

This table shows all possible conversions between types:

Target Type ↓ 

Source Type →

Additional information, notes, and examples

string*

number

integer

boolean

date

interval

string

✓

✓

✓

✓

✓

✓

Universal conversion target.

number

✓

✓

✓

❌

❌

❌

  • "1" → 1.0

  • 1 → 1.0

  • Strings must contain valid numeric values.

integer

✓

✓

✓

❌

❌

❌

  • "2" → 2

  • 2.5 → 2

  • Numbers are truncated, not rounded.

boolean

✓

✓

✓

✓

❌

❌

  • "true" → true

  • 1 → true

  • 0 → false

  • Non-zero numbers convert to true.

date

✓

✓

✓

❌

✓

❌

  • "2024-01-01" → 2024-01-01

  • 1704067200000 → 2024-01-01

  • When converting a number to a date, the number is interpreted as milliseconds since Unix epoch.

interval

✓

✓

✓

❌

❌

✓

  • "1h" → interval

  • 3600000 → "1h"

  • "60m" → "1h"

  • When converting a number to an interval, the number is interpreted as a duration in milliseconds. This represents a time span rather than a specific point in time.

*The conversion from string to a target type is done by parsing the string as a text representation of the target type.

Conversion Examples

Code Block
// Number conversion examples
number n1 = "42";     // String to number: 42.0
number n2 = 42;       // Integer to number: 42.0

// Integer conversion examples
integer i1 = "123";   // String to integer: 123
integer i2 = 123.7;   // Number to integer: 123 (truncated)

// Boolean conversion examples
boolean b1 = "true";  // String to boolean: true
boolean b2 = 1;       // Number to boolean: true
boolean b3 = 0;       // Number to boolean: false

// Date conversion examples
date d1 = "2024-01-01";        // String to date
date d2 = 1704067200000;       // Milliseconds to date

// Interval conversion examples
interval iv1 = "1h 30m";       // String to interval
interval iv2 = 5400000;        // Milliseconds to interval

When converting a string to an array type, the string is first transformed to a string[] by splitting it at every "|" character, and then the conversion is done from string []  to the target type array.

The conversion from string to a target type is done by parsing the string as a text representation of the target type.

Converting Arrays

Converting arrays of different types

Advanced Type Conversions

Array Conversion Rules

Array conversion is possible if the following conditions are met:

  • The element types (inner type of the array) are convertible

according to the the rules explained on this page. For example you

  • .

  • The conversion rules for array elements follow the same rules as single-value conversions explained earlier in this document.

  • All elements in the source array must be convertible to the target type.

Array Conversion Examples

You can cast a number[] to a string[] because number is convertible to string

, however

(Example 1). However you cannot convert a date[] to an interval[] because date cannot be converted to interval (Example 2).

Converting Structures

Structures can only be converted directly to string or an array type. Converting a structure to an array requires that each field of the structure is convertible to the element type (inner type) of the array.

Code Block
// Example 1: Number Array to String Array (Valid)
number[] numbers = [1, 2.5, 3.7, -4.2];
string[] stringNumbers = numbers;    // Valid conversion
// Result: ["1", "2.5", "3.7", "-4.2"]

// Example 2: Date Array to Interval Array (Invalid)
date[] dates = [
    "2024-01-01",
    "2024-01-02",
    "2024-01-03"
];
// interval[] periods = dates;    // This would cause a conversion error
                                 // Error: Cannot convert date to interval

String to Array Type Conversion Rules

When converting a string to an array, the process happens in two steps:

Step 1:

string → string[] and split on "|"

The string is first transformed to a string[] by splitting it at every "|" character.

Step 2:

string[] → target_type[]

The conversion is done from string[] to the target type array.

String Conversion Examples

Code Block
// Step 1: "1|2|3" → ["1", "2", "3"]
// Step 2: ["1", "2", "3"] → [1, 2, 3]

// Basic number array conversion
string numericString = "1|2|3|4|5";
number[] numbers = numericString;
// Result: [1.0, 2.0, 3.0, 4.0, 5.0]

// Basic boolean array conversion
string boolString = "true|false|true|true";
boolean[] flags = boolString;
// Result: [true, false, true, true]

Structure Conversion Rules

Structures can only be converted directly to string or arraytypes. It may be possible for certain structures to be convertible to other types by using one or more intermediate types

, however this is not done implicitly and users are required to use explicit casting in such cases. For

.

Structure to String Conversion

Conversions of this type follow these rules:

  • All fields are first converted to strings.

  • Fields are joined with commas.

Casting a structure to a string is equivalent to casting to a string[], and then the resulting array to string.

Code Block
// Define a simple structure
struct Person {
    string name;
    integer age;
    boolean isActive;
}

// Create and convert instance
Person person = { "John Smith", 30, true};

// Direct conversion to string
string personString = person;
return personString;
// Result: John Smith|30|true

Structure to Array Conversion

Conversions of this type follow these rules:

  • All structure fields must be convertible to the array's element type.

  • Fields are converted in order of declaration.

Code Block
// Structure with all number fields
struct Point3D {
    number x;
    number y;
    number z;
}

Point3D point = { 1.5, 2.0, 3.5 };

// Convert to number array (valid because all fields are numbers)
number[] coordinates = point;
// Result: [1.5, 2.0, 3.5]

// Convert to string array (always valid as all types can convert to string)
string[] stringCoords = point;
return stringCoords;
// Result: 1.5|2|3.5

Complex Conversions

Complex conversions (to types other than string/array) require:

  • Explicit intermediate steps

  • Manual casting between types

  • Fields that can ultimately convert to target type

Common common conversion patterns include:

  • Structure → string → target type

  • Structure → array → target type

In this example, a structure containing a single number field

may

can be converted to a number by first casting it to a string and then the resulting string to a number.

Tip

Casting a structure to a string is equivalent to casting to a string [] and then the resulting array to string.

Tip
titleCalling routines
When calling a routine or UDR, if the given parameter's type is not the same as what the routine is expecting, the conversion will be done automatically according to the rules above
Code Block
// Simple structure with a single numeric value
struct Temperature {
    number value;
}

// Create instance
Temperature temp = { 25.5 };

// GOAL: Convert the structure to a number

// Invalid: Direct conversion
// number n = temp;    // Error: Cannot convert structure to number

// Valid: Multi-step conversion
string tempStr = temp;           // Step 1: Structure to string ("25.5")
number tempValue = tempStr;      // Step 2: String to number (25.5)

// Alternative using array
string[] tempArray = temp;       // Step 1: Structure to string array (["25.5"])
number tempValue2 = tempArray[0];// Step 2: First array element to number (25.5)

// Using explicit casts (more verbose but clearer)
number explicitValue = (number)((string)temp);

Automatic Parameter Type Conversion

When calling functions (routines or UDRs), parameters are automatically converted to match the function’s expected parameter types, following the standard type conversion rules.

Code Block
function f(string s){
 
   print(s);
}
f(2); //number automatically converted to string
f(true); // boolean automatically converted to string
Info
titleCompatibility

These conversions cover the functionality implemented before v2.5, so they are backwards compatible.

Contents

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