All genuine ('natural') opening bids of a suit promise at least 4-cards in that suit.
In the 5-card major system of bidding it is possible to hold a balanced 4-4-3-2 hand containing 4-card suits in both Spades and Hearts, and only 3 cards and 2 cards in Diamonds and Clubs (or vice versa). Opening 1 Spade or 1 Heart is not possible with those hands and an opening bid of 1 Diamond or 1 Club must be made.
- Better minor
Many players prefer in such cases to bid their better minor suit, showing therefore at least 3 cards in that suit.
- Short Club
In this Course I have opted for the other solution, where and opening bid of 1 Diamond always promises at least 4 cards in that suit. Consequently a 1 Club opening bid may be based on only 2 cards in that suit.
This approach has the advantage that the 1 Diamond opening always is a genuine suit bid, and only one bid (the 1 Club opening) is ambiguous.
This solution also has the advantage that with a weak hand (and no other options) responder can confidently raise partner's 1 Diamond opening bid (to 2 Diamonds) with only 4 cards in Diamonds. To raise partner's 1 Club opening a 5-card Club suit is always required.
You may opt for either of above solutions as long as you and your partner are consistent in your approach.