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is vs ==
Aug 31
monkyyy
Aug 31
IchorDev
August 30
Gravatar of Brother BillPosted by Brother BillReply
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For the modern D developer, which is the more preferred choice, to use 'is' or '=='?

Do the Style Guidelines or other authorities prefer one to the other for modern D coding?

Or is either equally satisfactory?

August 31
Gravatar of monkyyyPosted by monkyyy
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On Saturday, 30 August 2025 at 22:15:26 UTC, Brother Bill wrote:

>

For the modern D developer, which is the more preferred choice, to use 'is' or '=='?

Do the Style Guidelines or other authorities prefer one to the other for modern D coding?

Or is either equally satisfactory?

different things is is mostly a special case like is null

August 31
Gravatar of Steven SchveighofferPosted by Steven Schveighoffer
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On Saturday, 30 August 2025 at 22:15:26 UTC, Brother Bill wrote:

>

For the modern D developer, which is the more preferred choice, to use 'is' or '=='?

is will do a direct bitwise comparison of the two sides, and cannot be hooked with an operator overload. This tests for identity (are the two sides the same instance).

== will use a type-specific comparison controlled by either the lhs type or the rhs type. This tests for logical equality.

>

Do the Style Guidelines or other authorities prefer one to the other for modern D coding?

Or is either equally satisfactory?

For value types that do not hook logical equality, is and == can be the same operation. There are some exceptions, for example floating-point numbers.

is is generally preferred for pointer or reference comparisons.

-Steve

August 31
Gravatar of IchorDevPosted by IchorDev
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On Saturday, 30 August 2025 at 22:15:26 UTC, Brother Bill wrote:

>

Do the Style Guidelines or other authorities prefer one to the other for modern D coding?

No: https://dlang.org/dstyle.html

>

For the modern D developer, which is the more preferred choice, to use 'is' or '=='?

This question doesn't make much sense. It's like if you asked the same thing about delegates vs functions.
is tells you if its operands are exact bit-for-bit matches, whereas == usually compares the contents of two things and may be overloaded using opCmp or opEquals.
For clarity's sake, is should generally be used for pointer comparison.

August 31
Gravatar of H. S. TeohPosted by H. S. Teoh
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On Sat, Aug 30, 2025 at 10:15:26PM +0000, Brother Bill via Digitalmars-d-learn wrote:
> For the modern D developer, which is the more preferred choice, to use 'is' or '=='?
[...]

They have two different meanings.  `is` is for determining identity (is this the same variable); whereas `==` is for comparing values (do these two variables have the same value).  They are not interchangeable.


T

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