# Compilation Error: Generic class with instance var of array of class type with generic parameter

**URL:** <https://forum.crystal-lang.org/t/compilation-error-generic-class-with-instance-var-of-array-of-class-type-with-generic-parameter/3284>\
**Category:** Help & Support\
**Created:** [May 8, 2021, 10:29am UTC](https://forum.crystal-lang.org/t/compilation-error-generic-class-with-instance-var-of-array-of-class-type-with-generic-parameter/3284 "2021-05-08T10:29:41Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Ragmaanir](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/ragmaanir/32/1174_2.png) [@Ragmaanir](https://forum.crystal-lang.org/u/Ragmaanir)\
**Post date:** [May 8, 2021, 10:29am UTC](https://forum.crystal-lang.org/t/compilation-error-generic-class-with-instance-var-of-array-of-class-type-with-generic-parameter/3284/1 "2021-05-08T10:29:41Z")

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I get a compilation error with this code:

```crystal
class Cmd(C)
end

class Adm < Cmd(Int32)
end

class Ns(C)
  getter cmds : Array(Cmd(C).class) = Array(Cmd(C).class).new
end

ns = Ns(Int32).new

```

See: [Carcin](https://play.crystal-lang.org/#/r/b37f)

Error:

```
instance variable '@cmds' of Ns(Int32) must be Array(Cmd(C).class), not Array(Cmd(Int32).class)

```

If i change the array type by removing “.class”, then it compiles. I am unsure about what is wrong with this.

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<div class="post-metadata">

**Author:** ![erdnaxeli](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/erdnaxeli/32/1242_2.png) [@erdnaxeli](https://forum.crystal-lang.org/u/erdnaxeli)\
**Post date:** [May 8, 2021, 10:38am UTC](https://forum.crystal-lang.org/t/compilation-error-generic-class-with-instance-var-of-array-of-class-type-with-generic-parameter/3284/2 "2021-05-08T10:38:42Z")

</div>

I am not sure what is going out but if you remove `Adm` then your code compiles 🤔

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<div class="post-metadata">

**Author:** ![asterite](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/asterite/32/60_2.png) [@asterite](https://forum.crystal-lang.org/u/asterite)\
**Post date:** [May 8, 2021, 11:07am UTC](https://forum.crystal-lang.org/t/compilation-error-generic-class-with-instance-var-of-array-of-class-type-with-generic-parameter/3284/3 "2021-05-08T11:07:07Z")

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Please report a bug. Thank you!

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<div class="post-metadata">

**Author:** ![Ragmaanir](https://yyz2.discourse-cdn.com/flex036/user_avatar/forum.crystal-lang.org/ragmaanir/32/1174_2.png) [@Ragmaanir](https://forum.crystal-lang.org/u/Ragmaanir)\
**Post date:** [May 8, 2021, 11:15am UTC](https://forum.crystal-lang.org/t/compilation-error-generic-class-with-instance-var-of-array-of-class-type-with-generic-parameter/3284/4 "2021-05-08T11:15:40Z")

</div>

Done: [Compilation Error: Generic class with instance var of array of class type with generic parameter · Issue #10691 · crystal-lang/crystal · GitHub](https://github.com/crystal-lang/crystal/issues/10691)