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Scala
Scala's Type System: a tutorial
Published: 2012/04/01
Channel: Ben Hutchison
Nerd³ Makes... Systems Nominal
Nerd³ Makes... Systems Nominal
Published: 2015/01/03
Channel: OfficialNerdCubed
Data Types C# - common language runtime types, nominal storage allocation, and value range
Data Types C# - common language runtime types, nominal storage allocation, and value range
Published: 2014/09/26
Channel: Damien Kettle
Types of Accounts : Personal Account, Real Account, Nominal Account
Types of Accounts : Personal Account, Real Account, Nominal Account
Published: 2015/12/21
Channel: Online Accounts Tuition Classes
Live Sound 101: Analog Audio Signal Types
Live Sound 101: Analog Audio Signal Types
Published: 2013/02/16
Channel: BigNate84
Analysis of Medium Transmission Lines
Analysis of Medium Transmission Lines
Published: 2015/07/16
Channel: Ravichandran Sekar
Real GDP and nominal GDP | GDP: Measuring national income | Macroeconomics | Khan Academy
Real GDP and nominal GDP | GDP: Measuring national income | Macroeconomics | Khan Academy
Published: 2012/02/10
Channel: Khan Academy
TDT01:  Introduction to Transmission Lines
TDT01: Introduction to Transmission Lines
Published: 2012/01/19
Channel: Greg Durgin
System Dynamics and Control: Module 2c - Static vs. Dynamic Models
System Dynamics and Control: Module 2c - Static vs. Dynamic Models
Published: 2016/08/17
Channel: Rick Hill
Floating vs. Fixed Exchange Rates- Macroeconomics 5.4
Floating vs. Fixed Exchange Rates- Macroeconomics 5.4
Published: 2014/11/11
Channel: ACDCLeadership
Identifying Thread Pitch & Size
Identifying Thread Pitch & Size
Published: 2012/02/22
Channel: swagelok
Limits and Fits, Selecting Size Tolerances
Limits and Fits, Selecting Size Tolerances
Published: 2010/01/28
Channel: GeoTolPro
Type-Z.E.R.O. - All Systems Nominal
Type-Z.E.R.O. - All Systems Nominal
Published: 2013/02/03
Channel: Eric Normandin
Look inside Athena Technologies Audition AS-C1 Center Speaker
Look inside Athena Technologies Audition AS-C1 Center Speaker
Published: 2017/06/14
Channel: ArtūrsM
Money supply: M0, M1, and M2 | The monetary system | Macroeconomics | Khan Academy
Money supply: M0, M1, and M2 | The monetary system | Macroeconomics | Khan Academy
Published: 2012/03/23
Channel: Khan Academy
Types of Variables
Types of Variables
Published: 2010/07/06
Channel: statslectures
Lecture - 10 Transmission Line Parameters
Lecture - 10 Transmission Line Parameters
Published: 2008/01/26
Channel: nptelhrd
Systems Nominal: I Cant Type!
Systems Nominal: I Cant Type!
Published: 2014/12/23
Channel: DeathAngelGaming
RingCentral Review: Getting Started Demo & Tutorial
RingCentral Review: Getting Started Demo & Tutorial
Published: 2015/04/12
Channel: Seth Williams
Data Types, Constructors and Common type system  in Microsoft .Net
Data Types, Constructors and Common type system in Microsoft .Net
Published: 2015/07/22
Channel: Microsoft .Net
First Normal Form | Database Management System
First Normal Form | Database Management System
Published: 2014/09/30
Channel: Techtud
Advanced English Grammar: Noun Clauses
Advanced English Grammar: Noun Clauses
Published: 2016/07/12
Channel: English Lessons with Adam - Learn English with Adam [engVid]
Systems Nominal (Anything But)
Systems Nominal (Anything But)
Published: 2014/12/24
Channel: Kyoto-Moto
Energy rc-50b-1 Harman/Kardon 3300 Receiver
Energy rc-50b-1 Harman/Kardon 3300 Receiver
Published: 2017/06/21
Channel: V. J
[MWO] All Systems Nominal
[MWO] All Systems Nominal
Published: 2012/11/09
Channel: John Garren
Type-Z.E.R.O. - All Systems Nominal (OCD-13001)
Type-Z.E.R.O. - All Systems Nominal (OCD-13001)
Published: 2013/02/01
Channel: Overdrive Canada
Type-ZERO - All Systems Nominal (MechWarrior Online Tribute)
Type-ZERO - All Systems Nominal (MechWarrior Online Tribute)
Published: 2013/01/02
Channel: Eric Normandin
Lecture - 26 Load Flow Studies
Lecture - 26 Load Flow Studies
Published: 2008/01/28
Channel: nptelhrd
What is DICHOTOMY? What does DICHOTOMY mean? DICHOTOMY meaning, definition & explanation
What is DICHOTOMY? What does DICHOTOMY mean? DICHOTOMY meaning, definition & explanation
Published: 2017/01/25
Channel: The Audiopedia
Indie Plays Systems Nominal - Learning to touch type really badly!
Indie Plays Systems Nominal - Learning to touch type really badly!
Published: 2015/01/07
Channel: Games Defined
SPSS for questionnaire analysis:  Correlation analysis
SPSS for questionnaire analysis: Correlation analysis
Published: 2013/12/24
Channel: Phil Chan
All Systems Nominal: Stagger #7
All Systems Nominal: Stagger #7
Published: 2015/03/05
Channel: NoGutsNoGalaxyTV
What Is Personal Real And Nominal Account?
What Is Personal Real And Nominal Account?
Published: 2017/06/20
Channel: smART X-mas
All Systems Nominal: CW Chapter 2
All Systems Nominal: CW Chapter 2
Published: 2015/04/15
Channel: NoGutsNoGalaxyTV
Macroeconomics: Crash Course Economics #5
Macroeconomics: Crash Course Economics #5
Published: 2015/08/24
Channel: CrashCourse
Logoster Plays: Systems Nominal
Logoster Plays: Systems Nominal
Published: 2014/12/24
Channel: TheGamingChannel
All Systems Nominal: Episode #6 - Retroactive
All Systems Nominal: Episode #6 - Retroactive
Published: 2014/11/04
Channel: NoGutsNoGalaxyTV
Siemens 5TA4707
Siemens 5TA4707
Published: 2017/06/21
Channel: eibmarkt.com GmbH
Continuous Vs. Discrete Data
Continuous Vs. Discrete Data
Published: 2014/12/29
Channel: Fast Math
Siemens DE 04101 M
Siemens DE 04101 M
Published: 2017/06/21
Channel: eibmarkt.com GmbH
SQL Normalization - The Basics - 1st, 2nd, 3rd Normal Form Software Engineering Tutorial
SQL Normalization - The Basics - 1st, 2nd, 3rd Normal Form Software Engineering Tutorial
Published: 2011/10/25
Channel: Edward Kench
Multi strand system.avi
Multi strand system.avi
Published: 2012/03/30
Channel: EPTGROUP
All Systems Nominal: Phase 3 Teaser
All Systems Nominal: Phase 3 Teaser
Published: 2016/06/25
Channel: PLEXI
Nissan CVT: Teardown and Failure Analysis - Part 1
Nissan CVT: Teardown and Failure Analysis - Part 1
Published: 2017/06/20
Channel: Pine Hollow Auto Diagnostics
All systems nominal
All systems nominal
Published: 2013/09/28
Channel: ShooterXGR
Vater Nicht - All Systems Nominal
Vater Nicht - All Systems Nominal
Published: 2013/07/24
Channel: Vater Nicht
Aluminum Foil with Embossing rewinding Machines Manufacturer
Aluminum Foil with Embossing rewinding Machines Manufacturer
Published: 2017/03/06
Channel: Ocean International
Hera 20202720108
Hera 20202720108
Published: 2017/06/21
Channel: eibmarkt.com GmbH
pad printing machine, date printer, logo marking system
pad printing machine, date printer, logo marking system
Published: 2014/08/13
Channel: Tru Mark Enterprises INDIA
Systems of Government:  Unitary, Federal, and Confederal
Systems of Government: Unitary, Federal, and Confederal
Published: 2014/09/03
Channel: Brad Cartwright Economics
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WIKIPEDIA ARTICLE

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In computer science, a nominal or nominative type system (or name-based type system) is a major class of type system, in which compatibility and equivalence of data types is determined by explicit declarations and/or the name of the types. Nominal systems are used to determine if types are equivalent, as well as if a type is a subtype of another. It contrasts with structural systems, where comparisons are based on the structure of the types in question and do not require explicit declarations.

Nominal typing[edit]

Nominal typing means that two variables are type-compatible if and only if their declarations name the same type. For example, in C, two struct types with different names in the same translation unit are never considered compatible, even if they have identical field declarations.

However, C also allows a typedef declaration, which introduces an alias for an existing type. These are merely syntactical and do not differentiate the type from its alias for the purpose of type checking. This feature, present in many languages, can result in a loss of type safety when (for example) the same primitive integer type is used in two semantically distinct ways. Haskell provides the C-style syntactic alias in the form of the type declaration, as well as the newtype declaration that does introduce a new, distinct type, isomorphic to an existing type.[1]

Nominal subtyping[edit]

In a similar fashion, nominal subtyping means that one type is a subtype of another if and only if it is explicitly declared to be so in its definition. Nominally-typed languages typically enforce the requirement that declared subtypes be structurally compatible (though Eiffel allows non-compatible subtypes to be declared). However, subtypes which are structurally compatible "by accident", but not declared as subtypes, are not considered to be subtypes.

C++, C#, Java, Objective-C, Delphi, Swift, and Rust all primarily use both nominal typing and nominal subtyping.

Some nominally-subtyped languages, such as Java and C#, allow classes to be declared final (or sealed in C# terminology), indicating that no further subtyping is permitted.

Comparison[edit]

Nominal typing is useful at preventing accidental type equivalence, which allows better type-safety than structural typing. The cost is a reduced flexibility, as, for example, nominal typing does not allow new super-types to be created without modification of the existing subtypes.

See also[edit]

Notes[edit]

References[edit]

External links[edit]

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