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template expressions

template_expressions #

Table of Contents

Introduction
Using the Library
Template Expression Syntax

HashExpressionSyntax
MustacheExpressionSyntax
PipeExpressionSyntax
StandardExpressionSyntax

Built in Objects and Members

Codex

Example
Member Functions

Crypto

Example

DateFormat

Constructors
Member Functions

DateTime

Constructors
Global Functions
Member Functions

Duration

Constructors
Global Functions
Member Functions

Encrypt

Example
Member Functions

Iterable

Member Functions
List
Member Functions
Int List Member Functions

JsonPath

Constructors
Global Functions
Member Functions

JsonPathMatch

Member Functions

Map

Member Functions

MapEntry

Member Functions

num

Member Functions

random

Example

String

Member Functions
Custom Functions

Object

Member Functions

Introduction #
A Dart library to process string based templates using expressions.
Using the Library #
Add the repo to your Dart pubspec.yaml file.
dependencies:
template_expressions: <<version>>
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Then run...
dart pub get
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Template Expression Syntax #
The template engine supports different syntax options for how the expressions are discovered within the template. There are three built in syntax options as described below. To provide your own syntax, simple implement the ExpressionSyntax class and pass that to the template at construction.
HashExpressionSyntax #
The hash expression syntax begins and ends with a double hash symbol. This syntax is compatible with many different forms of code and text file templates without much need for escape characters.
Example
{
"firstName": "##firstName.toUpperCase()##",
"lastName": "##lastName.toUpperCase()##"
}
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MustacheExpressionSyntax #
The mustache expression syntax begins with a double open curly brace and ends with a double close curley brace. This syntax is relatively common as it is a highly simplified version of the mustache template. Only the double curly braces are supported, no other aspects of the mustache syntax are.
Example
{
"firstName": "{{firstName.toUpperCase()}}",
"lastName": "{{lastName.toUpperCase()}}"
}
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PipeExpressionSyntax #
The pipe expression syntax begins and ends with a single pipe symbol. This syntax is compatible with many different forms of code and text file templates without much need for escape characters.
Example
{
"firstName": "|firstName.toUpperCase()|",
"lastName": "|lastName.toUpperCase()|"
}
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StandardExpressionSyntax #
The standard expression syntax follows the Dart string interpolation pattern. This is the default syntax all templates will use unless a separate syntax list is provided. It is the default as it is likely to be the most familiar with Dart developers, however it also has some conflicts that require special escaping. In Dart code, either the dollar sign must be escaped \${...} or the string must be tagged as a regular string (r'...'). In all forms, if there is a map defined in the expression, the close curly braces must be escaped like: r'${createName({"firstName": "John", "lastName": "Smith"\})}
Example
{
"firstName": "${firstName.toUpperCase()}",
"lastName": "${lastName.toUpperCase()}"
}
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Built in Objects and Members #
Codex #
The Codex class is supported for encoding and decoding values.
Example
base64.encode(value)
base64url.encode(value)
hex.encode(value)
json.encode(value)
utf8.encode(value)

base64.decode(value)
base64url.decode(value)
hex.decode(value)
json.decode(value)
utf8.decode(value)
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Member Functions

Function
Example

decode
${base64.decode(value)}

encode
${base64.encode(value)}

Crypto #
The Crypto functions exist for things like md5, sha256, sha512, and hmac functionality. Each function returns a lower case HEX encoded string of the resulting hash.
Example
md5(string)

hmac(secret, message) // synonym to hmac256
hmac256(secret, message) // synonym to hmac
hmac512(secret, message)

sha(string) // synonym to sha256
sha256(string) // synonym to sha
sha512(string)
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DateFormat #
The DateFormat class is supported for parsing and formatting functions.
Constructors
DateFormat(String format)
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Member Functions

Function
Example

format
${DateFormat('yyyy-MM-dd').format(now())}

parse
${DateFormat('yyyy-MM-dd').parse('2022-01-01')}

parseUTC
${DateFormat('yyyy-MM-dd').parseUTC('2022-01-01')}

parseUtc
${DateFormat('yyyy-MM-dd').parseUtc('2022-01-01')}

DateTime #
The DateTime class is supported for performing date time related functionality.
Constructors
now()
DateTime(int utcMillis)
DateTime(int year, int month, [int date, int hour, int minute, int second, int millisecond])
DateTime({int year, int month, int date, int hour, int minute, int second, int millisecond})
DateTime(List<int> yearMonthDateHourMinuteSecondMillisecond)
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Global Functions

Function
Description
Example

now
Alias for the dart code of DateTime.now()
${now()}

Member Functions

Function
Example

add
${now().add(minutes(5))}

add(int millis)
${now().add(30000)}

compareTo
${now().compareTo(other)}

isAfter
${now().isAfter(other)}

isBefore
${now().isBefore(other)}

isUtc
${now().isUtc}

millisecondsSinceEpoch
${now().millisecondsSinceEpoch}

subtract
${now().subtract(minutes(5))}

subtract(int millis)
${now().subtract(30000)}

toIso8601String
${now().toIso8601String()}

toLocal
${now().toLocal()}

toUtc
${now().toUtc()}

Duration #
The Duration class is supported for duration related calculations.
Constructors
now()
Duration(int milliseconds)
DateFormat(int days, int hours, [int minutes, int seconds, int milliseconds])
DateFormat({int days, int hours, [int minutes, int seconds, int milliseconds})
DateFormat(List<int> daysHoursMinutesSecondsMilliseconds)
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Global Functions

Function
Description
Example

days(int value)
Alias for Duration({"days": value})
${days(5).inMilliseconds}

hours(int value)
Alias for Duration({"hours": value})
${hours(5).inMilliseconds}

milliseconds(int value)
Alias for Duration({"milliseconds": value})
${milliseconds(5000).inSeconds}

minutes(int value)
Alias for Duration({"minutes": value})
${minutes(5).inMilliseconds}

seconds(int value)
Alias for Duration({"seconds": value})
${seconds(5).inMilliseconds}

Member Functions

Function
Example

add(Duration duration)
${Duration(1000).add(minutes(5))}

add(int milliseconds)
${Duration(1000).add(1000)}

compareTo
${Duration(1000).compareTo(other)}

inDays
${Duration({"hours": 48}).inDays}

inHours
${Duration(30000).inHours}

inMilliseconds
${Duration(30000).inMilliseconds}

inMinutes
${Duration(30000).inMinutes}

inSeconds
${Duration(30000).inSeconds}

subtract(Duration duration)
${Duration({minutes: 5}).subtract(seconds(5))}

subtract(int milliseconds)
${Duration({minutes: 5}).subtract(5000)}

Encrypt #
The Encrypt functions exist for AES and RSA cryptography functions.
Example
AES().key(key).encrypt(plainText)
AES().key(key).decrypt(encrypted)

RSA().publicKey(publicKey).encrypt(data).toBase64()
RSA().privateKey(privateKey).decrypt(data)

RSA().privateKey(privateKey).sign(data).toBase64()
RSA().publicKey(publicKey).verify(data, signature)
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Member Functions

Class
Function
Param(s)
Returns
Description

AES
key
(String | Uint8List | List<int> | SecureRandom: key)
AES
Sets the secret key on the AES object. If the input is a String, it must be base64 encoded.

AES
iv
(String | Uint8List | List<int> | IV: iv)
AES
Sets the IV on the AES object (should only be used for testing, for production code always use a generated IV and never a common one). If the input is a String, it must be base64 encoded.

AES
decrypt
(String: encrypted)
List<int>
Decrypts the value. Either the IV must be prior to calling this or it must be passed in base64 encoded at the start of the string followed by a colon and then the encrypted string. The encrypted string must also be base64 encoded

AES
encrypt
(String | Uint8List | List<int>: unencrypted)
String
Encrypts the passed in value, prepends the base64 encoded IV + : and returns the base64 encoded encrypted value.

RSA
publicKey
(String | RSAPublicKey: publicKey)
RSA
Accepts a String encoded PEM file or a public key object and sets it on the RSA object.

RSA
privateKey
(String | RSAPrivateKey: privateKey)
RSA
Accepts a String encoded PEM file or a private key object and sets it on the RSA object.

RSA
decrypt
(String
List<int>: encrypted)
Decrypts the value. This works by reversing the values from the RSA.encrypt.

RSA
encrypt
(String | Uint8List | List<int>: unencrypted)
String
This is a multi-step process. Either an AES object must have already been passed in, or a new one with a random key and random IV will be created. The key from the AES object will be encrypted using the RSA Public Key, base64 encoded, and added to the resulting key. Next the result from encrypting the value using AES will be appended to the returned string. The resulting string is: ${rsaEncryptedAesKey}:${aesIV}:${aesEncryptedValue}.

RSA
sign
String | Uint8List | List<int>
List<int>
Signs the given message and returns the bytes list.

RSA
verify
(String | Uint8List | List<int>: message, String | Uint8List | List<int>: signature)
List<int>
Signs the given message and returns the bytes list.

Iterable #
Several member functions from the Iterable class are supported.
Member Functions

Function
Example

contains
${value.contains('string')}

elementAt
${value.elementAt(1)}

first
${value.first}

isEmpty
${value.isEmpty ? 'null' : value.first}

isNotEmpty
${value.isNotEmpty ? value.first : 'null'}

last
${value.last}

length
${value.length}

join
${value.join(',')}

single
${value.single}

skip
${value.skip(1).join(',')}

take
${value.take(3).join(',')}

toList
${value.toList().sort()}

toSet
${value.toSet().first}

List
In addition to the items supported by the Iterable class, a List additionally supports the following functions...
Member Functions

Function
Example

asMap
${list.asMap()[2]}

reversed
${list.reversed.first}

toJson([int padding])
${list.toJson(2)}

sort
${list.sort().first}

Additionally, if the list is a List<int> or a Uint8List then there are additional helper functions that can be used:
Int List Member Functions

Function
Description
Example

toBase64
Base64 encodes the byte array
${list.toBase64()}

toHex
Hex encodes the byte array
${list.toHex()}

toString
UTF8 encodes the byte array
${list.toString()}

JsonPath #
The JsonPath class is supported to allow for walking JSON-like values.
Constructors
JsonPath(String expression)
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Global Functions

Function
Description
Example

json_path(dynamic value, String path)
Alias for JsonPath(path).read(value).first.value
${json_path(object, '$.person.firstName')}

Member Functions

Function
Example

read
${JsonPath('$.person.firstName').read(obj).first.value}

readValues
${JsonPath('$.person.firstName').values(obj).first}

JsonPathMatch #
The JsonPathMatch class is supported to allow for walking JSON-like values. It is unlikely you will want to create this class yourself and it is expected it will come from using JsonPath.
Member Functions

Function
Example

parent
${JsonPath('$.person.firstName').read(obj).first.parent.value}

path
${JsonPath('$.person.firstName').read(obj).first.path}

value
${JsonPath('$.person.firstName').read(obj).first.value}

Map #
The following Map members are supported.
Member Functions

Function
Example

containsValue
${map.containsValue('value')}

keys
${map.keys.first}

isEmpty
${map.isEmpty ? 'null' : map.values.first}

isNotEmpty
${map.isNotEmpty ? map.values.first : 'null'}

length
${map.length}

remove
${map.remove('key')}

toJson([int padding])
${map.toJson(2)}

values
${map.values.first}

MapEntry #
The following MapEntry members are supported.
Member Functions

Function
Example

key
${entry.key}

value
${entry.value}

num #
The following num members are supported.
Member Functions

Function
Example

abs
${number.abs()}

ceil
${number.ceil()}

ceilToDouble
${number.ceilToDouble()}

clamp
${number.clamp(lower, upper)}

compareTo
${number.compareTo(other)}

floor
${number.floor()}

floorToDouble
${number.floorToDouble()}

isFinite
${number.isFinite}

isInfinte
${number.isInfinte}

isNaN
${number.isNaN}

isNegative
${number.isNegative}

remainder
${number.remainder(other)}

round
${number.round()}

roundToDouble
${number.roundToDouble}

sign
${number.sign}

toDouble
${number.toDouble()}

toInt
${number.toInt()}

toStringAsExponential
${number.toStringAsExponential(fractionDigits)}

toStringAsFixed
${number.toStringAsFixed(fractionDigits)}

toStringAsPrecision
${number.toStringAsPrecision(precision)}

truncate
${number.truncate()}

truncateToDouble
${number.truncateToDouble()}

random #
The random function will operate in two modes. If a number is passed in, it will return a random integer between 0 and that number - 1. Otherwise, it will return a random double that is greater or equal to 0 and less than 1.
Example
random(100) // returns 0 - 99
random() // returns >= 0 < 1
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String #
The following String members are supported.
Member Functions

Function
Example
Description

compareTo
${str.compareTo(other)}

contains
${str.contains('other')}

decode
${str.decode()["firstName"]}
Decodes the string first trying as JSON and second as YAML to convert it to a map or a list

endsWith
${str.endsWith('other')}

indexOf
${str.indexOf('other')}

isEmpty
${str.isEmpty ? 'null' : str}

isNotEmpty
${str.isNotEmpty ? str : 'null'}

lastIndexOf
${str.lastIndexOf('/')}

length
${str.length}

padLeft
${str.padLeft(2, ' ')}

padRight
${str.padRight(2, ' ')}

replaceAll
${str.replaceAll('other', 'foo')}

replaceFirst
${str.replaceFirst('other', 'foo')}

split
${str.split(',').join('\n')}

startsWith
${str.startsWith('other')}

substring
${str.substring(begin, end)}

toLowerCase
${str.toLowerCase()}

toUpperCase
${str.toUpperCase()}

trim
${str.trim()}

trimLeft
${str.trimLeft()}

trimRight
${str.trimRight()}

Custom Functions

Function
Description
Example

decode
Attempts to decode the string using both a JSON and a YAML parser. If either is successful, the resulting map or list is returned.
${str.decode()["firstName"]}

Object #
The following Object members are supported.
Member Functions

Function
Example

hashCode
${obj.hashCode}

runtimeType
${obj.runtimeType.toString()}

toString
${obj.toString()}