# Limitations of Orbs Contracts

Orbs contracts are written in the Go programming language.

To enhance security and enable multiple virtual chains in the Orbs blockchain, the smart contracts are limited compared to the Go language. Specifically, Orbs limits the features and packages of the language that are allowed to execute inside the Orbs Virtual Machine.

## Package Whitelist

All packages in Go are not allowed except for specific packages listed in the whitelist below:

```
// Orbs Contract SDK
"github.com/orbs-network/orbs-contract-sdk/go/sdk/v1"
"github.com/orbs-network/orbs-contract-sdk/go/sdk/v1/address"
"github.com/orbs-network/orbs-contract-sdk/go/sdk/v1/env"
"github.com/orbs-network/orbs-contract-sdk/go/sdk/v1/ethereum"
"github.com/orbs-network/orbs-contract-sdk/go/sdk/v1/events"
"github.com/orbs-network/orbs-contract-sdk/go/sdk/v1/safemath"
"github.com/orbs-network/orbs-contract-sdk/go/sdk/v1/safemath/safeuint32"
"github.com/orbs-network/orbs-contract-sdk/go/sdk/v1/safemath/safeuint64"
"github.com/orbs-network/orbs-contract-sdk/go/sdk/v1/safemath/safeuint256"
"github.com/orbs-network/orbs-contract-sdk/go/sdk/v1/service"
"github.com/orbs-network/orbs-contract-sdk/go/sdk/v1/state"

// Text
"strings"
"strconv"
"text/template"

// Time
"time"

// Binary
"bytes"
"encoding/binary"
"io"

// Encoding
"encoding/json"
"encoding/hex"
"encoding/base32"
"encoding/base64"

// Utils
"sort"
```

Trying to include any package **not** in that list results in a failed compilation of the smart contract.

## Time functions blacklist

While we enable the use of the time package for time manipulation, it contains several functions which would result in inconsistent and non-deterministic results in contracts, and thus they are blacklisted. These functions are:

```
"After"
"AfterFunc"
"Sleep"
"Tick"
"NewTimer"
"NewTicker"
"Now"
```

Using any of these functions results in a failed compilation of the smart contract.

{% hint style="info" %}
If you want the current time ('Now'), it is possible to use the contract SDK function `env.GetBlockTimestamp()`
{% endhint %}

## Blacklisted Features

Aside from a whitelist of the allowed packages, Orbs does not allow the usage of the following Go language features:

* Channels
* Goroutines (the `go` statement)
* The 'arrow' unary expression (`<-`)

Using any of the above features results in a failed compilation of the smart contract.


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