PHP: How to set an element of an array without extra code?

Question

Yii

Good day
There is a piece of code for SELECT fields (YII2 framework)

->dropDownList($structure_enum, [
    'class' => 'form__select',
    'style' => 'width: 100%;',
])

That is, roughly speaking, there is an array of data
How to transfer or not one more key to this array by condition, without fencing extra code above
I.e. write something like

->dropDownList($structure_enum, [
    'class' => 'form__select',
    'style' => 'width: 100%;',
    $structure_strict ? 'disabled' => 'disabled' : '',
])

The code itself is not working, but for the example it is understandable
PS Please do not offer a type option in the answers

$a = [
    'class' => 'form__select',
    'style' => 'width: 100%;',
];

if ($structure_strict) $a ['disabled'] = 'disabled';
.....
->dropDownList($structure_enum, $a)

Interested in the issue of brevity
PS
Thank you all for your answers
In general, either through array_merge or through array addition

Answer 1

As an option to glue arrays:

->dropDownList($structure_enum, array_merge(
  [ 'class' => 'form__select', 'style' => 'width: 100%;' ],
  ($structure_strict) ? [ 'disabled' => 'disabled' ] : []
))

Answer 2

<?php

->dropDownList($structure_enum, array_filter([
    'class' => 'form__select',
    'style' => 'width: 100%;',
    'disabled' => $structure_strict ? 'disabled' : false,
]));